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Faraday As A Discoverer

by John Tyndall

March, 1998  [Etext #1225]


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Faraday As A Discoverer, by John Tyndall




Contents.

Preface.

Chapter 1.
 Parentage: introduction to the royal institution:
 earliest experiments: first royal society paper: marriage.

Chapter 2. 
 Early researches: magnetic rotations: liquefaction of gases:
 heavy glass: Charles Anderson: contributions to physics.

Chapter 3. 
 Discovery of Magneto-electricity: Explanation of Argo's magnetism
 of rotation: Terrestrial magneto-electric induction:
 The extra current.

Chapter 4.
 Points of Character.

Chapter 5.
 Identity of electricities; first researches on electro-chemistry.

Chapter 6.
 Laws of electro-chemical decomposition.

Chapter 7. 
 Origin of power in the voltaic pile.

Chapter 8. 
 Researches on frictional electricity: induction: conduction:
 specific inductive capacity: theory of contiguous particles.

Chapter 9. 
 Rest needed--visit to Switzerland.

Chapter 10.
 Magnetization of light.

Chapter 11.
 Discovery of diamagnetism--researches on magne-crystallic action.

Chapter 12.
 Magnetism of flame and gases--atmospheric magnetism.

Chapter 13.
 Speculations: nature of matter: lines of force.

Chapter 14.
 Unity and convertibility of natural forces: theory of the
 electric current.

Chapter 15.
 Summary.

Chapter 16.
 Illustrations of Character.


 Preface to the fifth edition.

Daily and weekly, from all parts of the world, I receive publications
bearing upon the practical applications of electricity.  This great
movement, the ultimate outcome of which is not to be foreseen, had
its origin in the discoveries made by Michael Faraday, sixty-two
years ago.  From these discoveries have sprung applications of the
telephone order, together with various forms of the electric
telegraph.  From them have sprung the extraordinary advances made in
electrical illumination.  Faraday could have had but an imperfect
notion of the expansions of which his discoveries were capable. 
Still he had a vivid and strong imagination, and I do not doubt that
he saw possibilities which did not disclose themselves to the
general scientific mind.  He knew that his discoveries had their
practical side, but he steadfastly resisted the seductions of this
side, applying himself to the development of principles; being well
aware that the practical question would receive due development
hereafter.  

During my sojourn in Switzerland this year, I read through the
proofs of this new edition, and by my reading was confirmed in the
conviction that the book ought not to be suffered to go out of
print.  The memoir was written under great pressure, but I am not
ashamed of it as it stands.  Glimpses of Faraday's character and
gleams of his discoveries are there to be found which will be of
interest to humanity to the end of time.

John Tyndall.
Hind Head,
December, 1893.



 [Note.--It was, I believe, my husband's intention to substitute
this Preface, written a few days before his death, for all former
Prefaces.  As, however, he had not the opportunity of revising the
old prefatory pages himself, they have been allowed to remain just
as they stood in the last edition.

Louisa C. Tyndall.] 


 Preface to the fourth edition.

When consulted a short time ago as to the republication of 'Faraday
as a Discoverer,' it seemed to me that the labours, and points of
character, of so great a worker and so good a man should not be
allowed to vanish from the public eye.  I therefore willingly fell
in with the proposal of my Publishers to issue a new edition of the
little book.

 Royal Institution,
 February, 1884.

 
 Preface to the second edition.

The experimental researches of Faraday are so voluminous,
their descriptions are so detailed, and their wealth of illustration
is so great, as to render it a heavy labour to master them.
The multiplication of proofs, necessary and interesting when the new
truths had to be established, are however less needful now when
these truths have become household words in science.  I have
therefore tried in the following pages to compress the body, without
injury to the spirit, of these imperishable investigations, and to
present them in a form which should be convenient and useful to the
student of the present day.

While I write, the volumes of the Life of Faraday by Dr. Bence
Jones have reached my hands.  To them the reader must refer for an
account of Faraday's private relations.  A hasty glance at the work
shows me that the reverent devotion of the biographer has turned to
admirable account the materials at his command.  

The work of Dr. Bence Jones enables me to correct a statement
regarding Wollaston's and Faraday's respective relations to the
discovery of Magnetic Rotation.  Wollaston's idea was to make the
wire carrying a current rotate round its own axis: an idea
afterwards realised by the celebrated Ampere. Faraday's discovery
was to make the wire carrying the current revolve round the pole of
a magnet and the reverse.

John Tyndall.
Royal Institution:
December, 1869.




FARADAY AS A DISCOVERER.

Chapter 1.

Parentage: introduction to the royal institution:
earliest experiments: first royal society paper: marriage.

It has been thought desirable to give you and the world some image
of MICHAEL FARADAY, as a scientific investigator and discoverer.
The attempt to respond to this desire has been to me a labour of
difficulty, if also a labour of love.  For however well acquainted
I may be with the researches and discoveries of that great
master--however numerous the illustrations which occur to me of the
loftiness of Faraday's character and the beauty of his life--still
to grasp him and his researches as a whole; to seize upon the ideas
which guided him, and connected them; to gain entrance into that
strong and active brain, and read from it the riddle of the world--
this is a work not easy of performance, and all but impossible amid
the distraction of duties of another kind.  That I should at one
period or another speak to you regarding Faraday and his work is
natural, if not inevitable; but I did not expect to be called upon
to speak so soon.  Still the bare suggestion that this is the fit
and proper time for speech sent me immediately to my task: from it
I have returned with such results as I could gather, and also with
the wish that those results were more worthy than they are of the
greatness of my theme.

It is not my intention to lay before you a life of Faraday in the
ordinary acceptation of the term.  The duty I have to perform is
to give you some notion of what he has done in the world; dwelling
incidentally on the spirit in which his work was executed,
and introducing such personal traits as may be necessary to the
completion of your picture of the philosopher, though by no means
adequate to give you a complete idea of the man.

The newspapers have already informed you that Michael Faraday was
born at Newington Butts, on September 22, 1791, and that he died at
Hampton Court, on August 25, 1867.  Believing, as I do, in the
general truth of the doctrine of hereditary transmission--sharing
the opinion of Mr. Carlyle, that 'a really able man never proceeded
from entirely stupid parents'--I once used the privilege of my
intimacy with Mr. Faraday to ask him whether his parents showed any
signs of unusual ability. He could remember none.  His father,
I believe, was a great sufferer during the latter years of his life,
and this might have masked whatever intellectual power he possessed. 
When thirteen years old, that is to say in 1804, Faraday was
apprenticed to a bookseller and bookbinder in Blandford Street,
Manchester Square: here he spent eight years of his life, after
which he worked as a journeyman elsewhere.

You have also heard the account of Faraday's first contact with the
Royal Institution; that he was introduced by one of the members to
Sir Humphry Davy's last lectures, that he took notes of those
lectures; wrote them fairly out, and sent them to Davy, entreating
him at the same time to enable him to quit trade, which he detested,
and to pursue science, which he loved. Davy was helpful to the young
man, and this should never be forgotten: he at once wrote to
Faraday, and afterwards, when an opportunity occurred, made him his
assistant.[1] Mr. Gassiot has lately favoured me with the following
reminiscence of this time:--

'Clapham Common, Surrey,
'November 28, 1867.

'My Dear Tyndall,--Sir H. Davy was accustomed to call on the late
Mr. Pepys, in the Poultry, on his way to the London Institution, of
which Pepys was one of the original managers; the latter told me
that on one occasion Sir H. Davy, showing him a letter, said:
"Pepys, what am I to do, here is a letter from a young man named
Faraday; he has been attending my lectures, and wants me to give him
employment at the Royal Institution--what can I do?" "Do?" replied
Pepys, "put him to wash bottles; if he is good for anything he will
do it directly, if he refuses he is good for nothing." "No, no,"
replied Davy; "we must try him with something better than that."
The result was, that Davy engaged him to assist in the Laboratory
at weekly wages.

'Davy held the joint office of Professor of Chemistry and Director
of the Laboratory; he ultimately gave up the former to the late
Professor Brande, but he insisted that Faraday should be appointed
Director of the Laboratory, and, as Faraday told me, this enabled
him on subsequent occasions to hold a definite position in the
Institution, in which he was always supported by Davy.
I believe he held that office to the last.

'Believe me, my dear Tyndall, yours truly,

'J.  P.  Gassiot.



'Dr. Tyndall.'

From a letter written by Faraday himself soon after his appointment
as Davy's assistant, I extract the following account of his
introduction to the Royal Institution:--
'London, Sept.  13, 1813.

'As for myself, I am absent (from home) nearly day and night, except
occasional calls, and it is likely shall shortly be absent entirely,
but this (having nothing more to say, and at the request of my
mother) I will explain to you.  I was formerly a bookseller and
binder, but am now turned philosopher,[2] which happened thus:--
Whilst an apprentice, I, for amusement, learnt a little chemistry
and other parts of philosophy, and felt an eager desire to proceed
in that way further.  After being a journeyman for six months,
under a disagreeable master, I gave up my business, and through
the interest of a Sir H. Davy, filled the situation of chemical
assistant to the Royal Institution of Great Britain, in which office
I now remain; and where I am constantly employed in observing the
works of nature, and tracing the manner in which she directs the
order and arrangement of the world.  I have lately had proposals
made to me by Sir Humphry Davy to accompany him in his travels
through Europe and Asia, as philosophical assistant.  If I go at all
I expect it will be in October next--about the end; and my absence
from home will perhaps be as long as three years.  But as yet all is
uncertain.'

This account is supplemented by the following letter, written by
Faraday to his friend De la Rive,[3] on the occasion of the death
of Mrs. Marcet. The letter is dated September 2, 1858:--

'My Dear Friend,--Your subject interested me deeply every way;
for Mrs. Marcet was a good friend to me, as she must have been to
many of the human race.  I entered the shop of a bookseller and
bookbinder at the age of thirteen, in the year 1804, remained there
eight years, and during the chief part of my time bound books. 
Now it was in those books, in the hours after work, that I found
the beginning of my philosophy.  

There were two that especially helped me, the "Encyclopaedia
Britannica," from which I gained my first notions of electricity,
and Mrs. Marcet's "Conversation on Chemistry," which gave me my
foundation in that science.

'Do not suppose that I was a very deep thinker, or was marked as a
precocious person.  I was a very lively imaginative person, and
could believe in the "Arabian Nights" as easily as in the
"Encyclopaedia." But facts were important to me, and saved me.
I could trust a fact, and always cross-examined an assertion.
So when I questioned Mrs. Marcet's book by such little experiments
as I could find means to perform, and found it true to the facts as
I could understand them, I felt that I had got hold of an anchor in
chemical knowledge, and clung fast to it.  Thence my deep veneration
for Mrs. Marcet--first as one who had conferred great personal good
and pleasure on me; and then as one able to convey the truth and
principle of those boundless fields of knowledge which concern
natural things to the young, untaught, and inquiring mind.

'You may imagine my delight when I came to know Mrs. Marcet
personally; how often I cast my thoughts backward, delighting to
connect the past and the present; how often, when sending a paper
to her as a thank-offering, I thought of my first instructress,
and such like thoughts will remain with me.  

'I have some such thoughts even as regards your own father; who was,
I may say, the first who personally at Geneva, and afterwards by
correspondence, encouraged, and by that sustained me.'

Twelve or thirteen years ago Mr. Faraday and myself quitted the
Institution one evening together, to pay a visit to our friend Grove
in Baker Street.  He took my arm at the door, and, pressing it to
his side in his warm genial way, said, 'Come, Tyndall, I will now
show you something that will interest you.' We walked northwards,
passed the house of Mr. Babbage, which drew forth a reference to the
famous evening parties once assembled there.  We reached Blandford
Street, and after a little looking about he paused before a
stationer's shop, and then went in.  On entering the shop, his usual
animation seemed doubled; he looked rapidly at everything it
contained.  To the left on entering was a door, through which he
looked down into a little room, with a window in front facing
Blandford Street.  Drawing me towards him, he said eagerly,
'Look there, Tyndall, that was my working-place. I bound books in
that little nook.' A respectable-looking woman stood behind the
counter: his conversation with me was too low to be heard by her,
and he now turned to the counter to buy some cards as an excuse for
our being there.  He asked the woman her name--her predecessor's
name-- his predecessor's name.  'That won't do,' he said, with
good-humoured impatience; 'who was his predecessor?' 'Mr. Riebau,'
she replied, and immediately added, as if suddenly recollecting
herself, 'He, sir, was the master of Sir Charles Faraday.'
'Nonsense!' he responded, 'there is no such person.' Great was her
delight when I told her the name of her visitor; but she assured me
that as soon as she saw him running about the shop, she felt-though
she did not know why--that it must be 'Sir Charles Faraday.'

Faraday did, as you know, accompany Davy to Rome: he was re-engaged
by the managers of the Royal Institution on May 15, 1815.  Here he
made rapid progress in chemistry, and after a time was entrusted
with easy analyses by Davy.  In those days the Royal Institution
published 'The Quarterly Journal of Science,' the precursor of our
own 'Proceedings.' Faraday's first contribution to science appeared
in that journal in 1816.  It was an analysis of some caustic lime
from Tuscany, which had been sent to Davy by the Duchess of Montrose.
Between this period and 1818 various notes and short papers
were published by Faraday.  In 1818 he experimented upon
'Sounding Flames.' Professor Auguste De la Rive had investigated
those sounding flames, and had applied to them an explanation which
completely accounted for a class of sounds discovered by himself,
but did not account for those known to his predecessors.  By a few
simple and conclusive experiments, Faraday proved the explanation
insufficient.  It is an epoch in the life of a young man when he
finds himself correcting a person of eminence, and in Faraday's
case, where its effect was to develop a modest self-trust, such an
event could not fail to act profitably.

From time to time between 1818 and 1820 Faraday published scientific
notes and notices of minor weight.  At this time he was acquiring,
not producing; working hard for his master and storing and
strengthening his own mind.  He assisted Mr. Brande in his lectures,
and so quietly, skilfully, and modestly was his work done, that
Mr. Brande's vocation at the time was pronounced 'lecturing on velvet.' 
In 1820 Faraday published a chemical paper 'on two new compounds of
chlorine and carbon, and on a new compound of iodine, carbon,
and hydrogen.'  This paper was read before the Royal Society on
December 21, 1820, and it was the first of his that was honoured
with a place in the 'Philosophical Transactions.' 

On June 12, 1821, he married, and obtained leave to bring his young
wife into his rooms at the Royal Institution.  There for forty-six
years they lived together, occupying the suite of apartments which
had been previously in the successive occupancy of Young, Davy, and
Brande. At the time of her marriage Mrs. Faraday was twenty-one
years of age, he being nearly thirty. Regarding this marriage I will
at present limit myself to quoting an entry written in Faraday's own
hand in his book of diplomas, which caught my eye while in his
company some years ago. It ran thus:--

'25th January, 1847.
'Amongst these records and events, I here insert the date of one
which, as a source of honour and happiness, far exceeds all the
rest.  We were married on June 12, 1821.

'M. Faraday.'

Then follows the copy of the minutes, dated May 21, 1821, which gave
him additional rooms, and thus enabled him to bring his wife to the
Royal Institution.  A feature of Faraday's character which I have
often noticed makes itself apparent in this entry.  In his relations
to his wife he added chivalry to affection.


Footnotes to Chapter 1

[1] Here is Davy's recommendation of Faraday, presented to the
managers of the Royal Institution, at a meeting on the 18th of
March, 1813, Charles Hatchett, Esq., in the chair:--

'Sir Humphry Davy has the honour to inform the managers that he has
found a person who is desirous to occupy the situation in the
Institution lately filled by William Payne.  His name is Michael
Faraday. He is a youth of twenty-two years of age.  As far as Sir H.
Davy has been able to observe or ascertain, he appears well fitted
for the situation.  His habits seem good; his disposition active and
cheerful, and his manner intelligent.  He is willing to engage
himself on the same terms as given to Mr. Payne at the time of
quitting the Institution.

'Resolved,--That Michael Faraday be engaged to fill the situation
lately occupied by Mr. Payne, on the same terms.'

[2] Faraday loved this word and employed it to the last; he had an
intense dislike to the modern term physicist.

[3] To whom I am indebted for a copy of the original letter.


Chapter 2.

Early researches: magnetic rotations: liquefaction of gases:
heavy glass: Charles Anderson: contributions to physics.

Oersted, in 1820, discovered the action of a voltaic current on a
magnetic needle; and immediately afterwards the splendid intellect
of Ampere succeeded in showing that every magnetic phenomenon then
known might be reduced to the mutual action of electric currents. 
The subject occupied all men's thoughts: and in this country
Dr. Wollaston sought to convert the deflection of the needle by the
current into a permanent rotation of the needle round the current. 
He also hoped to produce the reciprocal effect of causing a current
to rotate round a magnet. In the early part of 1821, Wollaston
attempted to realise this idea in the presence of Sir Humphry Davy
in the laboratory of the Royal Institution.[1] This was well
calculated to attract Faraday's attention to the subject.  He read
much about it; and in the months of July, August, and September he
wrote a 'history of the progress of electro-magnetism,' which he
published in Thomson's 'Annals of Philosophy.'  Soon afterwards he
took up the subject of 'Magnetic Rotations,' and on the morning of
Christmas-day, 1821, he called his wife to witness, for the first
time, the revolution of a magnetic needle round an electric current. 
Incidental to the 'historic sketch,' he repeated almost all the
experiments there referred to; and these, added to his own
subsequent work, made him practical master of all that was then
known regarding the voltaic current.  In 1821, he also touched upon
a subject which subsequently received his closer attention--the
vaporization of mercury at common temperatures; and immediately
afterwards conducted, in company with Mr. Stodart, experiments on
the alloys of steel.  He was accustomed in after years to present to
his friends razors formed from one of the alloys then discovered.

During Faraday's hours of liberty from other duties, he took up
subjects of inquiry for himself; and in the spring of 1823, thus
self-prompted, he began the examination of a substance which had
long been regarded as the chemical element chlorine, in a solid
form, but which Sir Humphry Davy, in 1810, had proved to be a
hydrate of chlorine, that is, a compound of chlorine and water. 
Faraday first analysed this hydrate, and wrote out an account of its
composition.  This account was looked over by Davy, who suggested
the heating of the hydrate under pressure in a sealed glass tube. 
This was done.  The hydrate fused at a blood-heat, the tube became
filled with a yellow atmosphere, and was afterwards found to contain
two liquid substances.  Dr. Paris happened to enter the laboratory
while Faraday was at work.  Seeing the oily liquid in his tube, he
rallied the young chemist for his carelessness in employing soiled
vessels.  On filing off the end of the tube, its contents exploded
and the oily matter vanished.  Early next morning, Dr. Paris
received the following note:--

'Dear Sir,--The oil you noticed yesterday turns out to be
liquid chlorine.

'Yours faithfully,
'M. Faraday.'[2]

The gas had been liquefied by its own pressure.  Faraday then tried
compression with a syringe, and succeeded thus in liquefying the gas.

To the published account of this experiment Davy added the following
note:--'In desiring Mr. Faraday to expose the hydrate of chlorine in
a closed glass tube, it occurred to me that one of three things
would happen: that decomposition of water would occur;... or that
the chlorine would separate in a fluid state.' Davy, moreover,
immediately applied the method of self-compressing atmosphere to the
liquefaction of muriatic gas.  Faraday continued the experiments,
and succeeded in reducing a number of gases till then deemed permanent
to the liquid condition.  In 1844 he returned to the subject, and
considerably expanded its limits.  These important investigations
established the fact that gases are but the vapours of liquids
possessing a very low boiling-point, and gave a sure basis to our
views of molecular aggregation.  The account of the first investigation
was read before the Royal Society on April 10, 1823, and was
published, in Faraday's name, in the 'Philosophical Transactions.'
The second memoir was sent to the Royal Society on December 19, 1844.
I may add that while he was conducting his first experiments on the
liquefaction of gases, thirteen pieces of glass were on one occasion
driven by an explosion into Faraday's eye.

Some small notices and papers, including the observation that glass
readily changes colour in sunlight, follow here.  In 1825 and 1826
Faraday published papers in the 'Philosophical Transactions' on
'new compounds of carbon and hydrogen,' and on 'sulphonaphthalic acid.'
In the former of these papers he announced the discovery of Benzol,
which, in the hands of modern chemists, has become the foundation of
our splendid aniline dyes.  But he swerved incessantly from chemistry
into physics; and in 1826 we find him engaged in investigating the
limits of vaporization, and showing, by exceedingly strong and
apparently conclusive arguments, that even in the case of mercury
such a limit exists; much more he conceived it to be certain that
our atmosphere does not contain the vapour of the fixed constituents
of the earth's crust. This question, I may say, is likely to remain
an open one.  Dr. Rankine, for example, has lately drawn attention
to the odour of certain metals; whence comes this odour, if it be
not from the vapour of the metal?

In 1825 Faraday became a member of a committee, to which Sir John
Herschel and Mr. Dollond also belonged, appointed by the Royal Society
to examine, and if possible improve, the manufacture of glass for
optical purposes. Their experiments continued till 1829, when the
account of them constituted the subject of a 'Bakerian Lecture.'
This lectureship, founded in 1774 by Henry Baker, Esq., of the
Strand, London, provides that every year a lecture shall be given
before the Royal Society, the sum of four pounds being paid to the
lecturer.  The Bakerian Lecture, however, has long since passed from
the region of pay to that of honour, papers of mark only being
chosen for it by the council of the Society.  Faraday's first
Bakerian Lecture, 'On the Manufacture of Glass for Optical Purposes,'
was delivered at the close of 1829.  It is a most elaborate and
conscientious description of processes, precautions, and results:
the details were so exact and so minute, and the paper consequently
so long, that three successive sittings of the Royal Society were
taken up by the delivery of the lecture.[3] This glass did not turn
out to be of important practical use, but it happened afterwards to
be the foundation of two of Faraday's greatest discoveries.[4]

The experiments here referred to were commenced at the Falcon Glass
Works, on the premises of Messrs.  Green and Pellatt, but Faraday
could not conveniently attend to them there.  In 1827, therefore,
a furnace was erected in the yard of the Royal Institution; and it
was at this time, and with a view of assisting him at the furnace,
that Faraday engaged Sergeant Anderson, of the Royal Artillery,
the respectable, truthful, and altogether trustworthy man whose
appearance here is so fresh in our memories.  Anderson continued to
be the reverential helper of Faraday and the faithful servant of
this Institution for nearly forty years.[5]

In 1831 Faraday published a paper, 'On a peculiar class of Optical
Deceptions,' to which I believe the beautiful optical toy called the
Chromatrope owes its origin.  In the same year he published a paper
on Vibrating Surfaces, in which he solved an acoustical problem
which, though of extreme simplicity when solved, appears to have
baffled many eminent men.  The problem was to account for the fact
that light bodies, such as the seed of lycopodium, collected at the
vibrating parts of sounding plates, while sand ran to the nodal
lines.  Faraday showed that the light bodies were entangled in the
little whirlwinds formed in the air over the places of vibration,
and through which the heavier sand was readily projected.  Faraday's
resources as an experimentalist were so wonderful, and his delight
in experiment was so great, that he sometimes almost ran into excess
in this direction.  I have heard him say that this paper on
vibrating surfaces was too heavily laden with experiments.


Footnotes to Chapter 2

[1] The reader's attention is directed to the concluding paragraph
of the 'Preface to the Second Edition written in December, 1869. 
Also to the Life of Faraday by Dr. Bence Jones, vol. i. p. 338 et seq.

[2] Paris: Life of Davy, p. 391.

[3] Viz., November 19, December 3 and 10.

[4] I make the following extract from a letter from Sir John Herschel,
written to me from Collingwood, on the 3rd of November, 1867:--

'I will take this opportunity to mention that I believe myself to
have originated the suggestion of the employment of borate of lead
for optical purposes.  It was somewhere in the year 1822, as well as
I can recollect, that I mentioned it to Sir James (then Mr.) South;
and, in consequence, the trial was made in his laboratory in
Blackman Street, by precipitating and working a large quantity of
borate of lead, and fusing it under a muffle in a porcelain
evaporating dish.  A very limpid (though slightly yellow) glass
resulted, the refractive index 1.866! (which you will find set down
in my table of refractive indices in my article "Light,"
Encyclopaedia Metropolitana).  It was, however, too soft for optical
use as an object-glass.  This Faraday overcame, at least to a
considerable degree, by the introduction of silica.'

[5] Regarding Anderson, Faraday writes thus in 1845:--'I cannot
resist the occasion that is thus offered to me of mentioning the
name of Mr. Anderson, who came to me as an assistant in the glass
experiments, and has remained ever since in the laboratory of the
Royal Institution.  He assisted me in all the researches into which
I have entered since that time; and to his care, steadiness,
exactitude, and faithfulness in the performance of all that has been
committed to his charge, I am much indebted.--M. F.' (Exp. Researches,
vol. iii. p. 3, footnote.)


Chapter 3.

Discovery of Magneto-electricity: Explanation of Argo's magnetism of
rotation: Terrestrial magneto-electric induction: The extra current.

The work thus referred to, though sufficient of itself to secure no
mean scientific reputation, forms but the vestibule of Faraday's
achievements.  He had been engaged within these walls for eighteen
years.  During part of the time he had drunk in knowledge from Davy,
and during the remainder he continually exercised his capacity for
independent inquiry.  In 1831 we have him at the climax of his
intellectual strength, forty years of age, stored with knowledge and
full of original power.  Through reading, lecturing, and experimenting,
he had become thoroughly familiar with electrical science: he saw
where light was needed and expansion possible.  The phenomena of
ordinary electric induction belonged, as it were, to the alphabet of
his knowledge: he knew that under ordinary circumstances the
presence of an electrified body was sufficient to excite, by
induction, an unelectrified body.  He knew that the wire which
carried an electric current was an electrified body, and still that
all attempts had failed to make it excite in other wires a state
similar to its own.

What was the reason of this failure?  Faraday never could work from
the experiments of others, however clearly described.  He knew well
that from every experiment issues a kind of radiation, luminous in
different degrees to different minds, and he hardly trusted himself
to reason upon an experiment that he had not seen.  In the autumn of
1831 he began to repeat the experiments with electric currents,
which, up to that time, had produced no positive result.  And here,
for the sake of younger inquirers, if not for the sake of us all,
it is worth while to dwell for a moment on a power which Faraday
possessed in an extraordinary degree.  He united vast strength with
perfect flexibility.  His momentum was that of a river, which
combines weight and directness with the ability to yield to the
flexures of its bed.  The intentness of his vision in any direction
did not apparently diminish his power of perception in other
directions; and when he attacked a subject, expecting results he had
the faculty of keeping his mind alert, so that results different
from those which he expected should not escape him through
preoccupation.  

He began his experiments 'on the induction of electric currents' by
composing a helix of two insulated wires which were wound side by
side round the same wooden cylinder.  One of these wires he connected
with a voltaic battery of ten cells, and the other with a sensitive
galvanometer.  When connection with the battery was made, and while
the current flowed, no effect whatever was observed at the
galvanometer.  But he never accepted an experimental result, until he
had applied to it the utmost power at his command.  He raised his
battery from 10 cells to 120 cells, but without avail.  The current
flowed calmly through the battery wire without producing, during its
flow, any sensible result upon the galvanometer.

'During its flow,' and this was the time when an effect was expected--
but here Faraday's power of lateral vision, separating, as it were,
from the line of expectation, came into play--he noticed that a
feeble movement of the needle always occurred at the moment when he
made contact with the battery; that the needle would afterwards
return to its former position and remain quietly there unaffected by
the flowing current.  At the moment, however, when the circuit was
interrupted the needle again moved, and in a direction opposed to
that observed on the completion of the circuit.  

This result, and others of a similar kind, led him to the conclusion
'that the battery current through the one wire did in reality induce
a similar current through the other; but that it continued for an
instant only, and partook more of the nature of the electric wave
from a common Leyden jar than of the current from a voltaic battery.'
The momentary currents thus generated were called induced currents,
while the current which generated them was called the inducing
current.  It was immediately proved that the current generated at
making the circuit was always opposed in direction to its generator,
while that developed on the rupture of the circuit coincided in
direction with the inducing current.  It appeared as if the current
on its first rush through the primary wire sought a purchase in the
secondary one, and, by a kind of kick, impelled backward through the
latter an electric wave, which subsided as soon as the primary
current was fully established.

Faraday, for a time, believed that the secondary wire, though
quiescent when the primary current had been once established, was
not in its natural condition, its return to that condition being
declared by the current observed at breaking the circuit.  He called
this hypothetical state of the wire the electro-tonic state: he
afterwards abandoned this hypothesis, but seemed to return to it in
later life.  The term electro-tonic is also preserved by Professor
Du Bois Reymond to express a certain electric condition of the nerves,
and Professor Clerk Maxwell has ably defined and illustrated the
hypothesis in the Tenth Volume of the 'Transactions of the Cambridge
Philosophical Society.'

The mere approach of a wire forming a closed curve to a second wire
through which a voltaic current flowed was then shown by Faraday to
be sufficient to arouse in the neutral wire an induced current,
opposed in direction to the inducing current; the withdrawal of the
wire also generated a current having the same direction as the
inducing current; those currents existed only during the time of
approach or withdrawal, and when neither the primary nor the
secondary wire was in motion, no matter how close their proximity
might be, no induced current was generated.

Faraday has been called a purely inductive philosopher.  A great deal
of nonsense is, I fear, uttered in this land of England about
induction and deduction.  Some profess to befriend the one, some the
other, while the real vocation of an investigator, like Faraday,
consists in the incessant marriage of both.  He was at this time full
of the theory of Ampere, and it cannot be doubted that numbers of
his experiments were executed merely to test his deductions from
that theory.  Starting from the discovery of Oersted, the illustrious
French philosopher had shown that all the phenomena of magnetism
then known might be reduced to the mutual attractions and repulsions
of electric currents.  Magnetism had been produced from electricity,
and Faraday, who all his life long entertained a strong belief in
such reciprocal actions, now attempted to effect the evolution of
electricity from magnetism.  Round a welded iron ring he placed two
distinct coils of covered wire, causing the coils to occupy opposite
halves of the ring.  Connecting the ends of one of the coils with a
galvanometer, he found that the moment the ring was magnetised, by
sending a current through the other coil, the galvanometer needle
whirled round four or five times in succession.  The action,
as before, was that of a pulse, which vanished immediately.
On interrupting the circuit, a whirl of the needle in the opposite
direction occurred.  It was only during the time of magnetization or
demagnetization that these effects were produced.  The induced
currents declared a change of condition only, and they vanished the
moment the act of magnetization or demagnetization was complete.

The effects obtained with the welded ring were also obtained with
straight bars of iron.  Whether the bars were magnetised by the
electric current, or were excited by the contact of permanent steel
magnets, induced currents were always generated during the rise,
and during the subsidence of the magnetism.  The use of iron was then
abandoned, and the same effects were obtained by merely thrusting a
permanent steel magnet into a coil of wire.  A rush of electricity
through the coil accompanied the insertion of the magnet; an equal
rush in the opposite direction accompanied its withdrawal.
The precision with which Faraday describes these results, and the
completeness with which he defines the boundaries of his facts,
are wonderful.  The magnet, for example, must not be passed quite
through the coil, but only half through; for if passed wholly
through, the needle is stopped as by a blow, and then he shows how
this blow results from a reversal of the electric wave in the helix. 
He next operated with the powerful permanent magnet of the Royal
Society, and obtained with it, in an exalted degree, all the
foregoing phenomena.

And now he turned the light of these discoveries upon the darkest
physical phenomenon of that day.  Arago had discovered, in 1824, that
a disk of non-magnetic metal had the power of bringing a vibrating
magnetic needle suspended over it rapidly to rest; and that on
causing the disk to rotate the magnetic needle rotated along with
it.  When both were quiescent, there was not the slightest measurable
attraction or repulsion exerted between the needle and the disk;
still when in motion the disk was competent to drag after it, not
only a light needle, but a heavy magnet.  The question had been
probed and investigated with admirable skill both by Arago and
Ampere, and Poisson had published a theoretic memoir on the subject;
but no cause could be assigned for so extraordinary an action.
It had also been examined in this country by two celebrated men,
Mr. Babbage and Sir John Herschel; but it still remained a mystery.
Faraday always recommended the suspension of judgment in cases of
doubt.  'I have always admired,' he says, 'the prudence and
philosophical reserve shown by M.  Arago in resisting the temptation
to give a theory of the effect he had discovered, so long as he
could not devise one which was perfect in its application, and in
refusing to assent to the imperfect theories of others.' Now,
however, the time for theory had come.  Faraday saw mentally the
rotating disk, under the operation of the magnet, flooded with his
induced currents, and from the known laws of interaction between
currents and magnets he hoped to deduce the motion observed by
Arago.  That hope he realised, showing by actual experiment that when
his disk rotated currents passed through it, their position and
direction being such as must, in accordance with the established
laws of electro-magnetic action, produce the observed rotation.

Introducing the edge of his disk between the poles of the large
horseshoe magnet of the Royal Society, and connecting the axis and
the edge of the disk, each by a wire with a galvanometer, he
obtained, when the disk was turned round, a constant flow of
electricity.  The direction of the current was determined by the
direction of the motion, the current being reversed when the
rotation was reversed.  He now states the law which rules the
production of currents in both disks and wires, and in so doing
uses, for the first time, a phrase which has since become famous.
When iron filings are scattered over a magnet, the particles of iron
arrange themselves in certain determinate lines called magnetic
curves.  In 1831, Faraday for the first time called these curves
'lines of magnetic force'; and he showed that to produce induced
currents neither approach to nor withdrawal from a magnetic source,
or centre, or pole, was essential, but that it was only necessary to
cut appropriately the lines of magnetic force.  Faraday's first paper
on Magneto-electric Induction, which I have here endeavoured to
condense, was read before the Royal Society on the 24th of November,
1831.

On January 12, 1832, he communicated to the Royal Society a second
paper on Terrestrial Magneto-electric Induction, which was chosen as
the Bakerian Lecture for the year.  He placed a bar of iron in a coil
of wire, and lifting the bar into the direction of the dipping needle,
he excited by this action a current in the coil.  On reversing the
bar, a current in the opposite direction rushed through the wire. 
The same effect was produced when, on holding the helix in the line
of dip, a bar of iron was thrust into it.  Here, however, the earth
acted on the coil through the intermediation of the bar of iron.
He abandoned the bar and simply set a copper plate spinning in a
horizontal plane; he knew that the earth's lines of magnetic force
then crossed the plate at an angle of about 70degrees.  When the plate
spun round, the lines of force were intersected and induced currents
generated, which produced their proper effect when carried from the
plate to the galvanometer.  'When the plate was in the magnetic
meridian, or in any other plane coinciding with the magnetic dip,
then its rotation produced no effect upon the galvanometer.'

At the suggestion of a mind fruitful in suggestions of a profound
and philosophic character--I mean that of Sir John Herschel--
Mr. Barlow, of Woolwich, had experimented with a rotating iron shell.
Mr. Christie had also performed an elaborate series of experiments
on a rotating iron disk.  Both of them had found that when in
rotation the body exercised a peculiar action upon the magnetic
needle, deflecting it in a manner which was not observed during
quiescence; but neither of them was aware at the time of the agent
which produced this extraordinary deflection.  They ascribed it to
some change in the magnetism of the iron shell and disk.

But Faraday at once saw that his induced currents must come into
play here, and he immediately obtained them from an iron disk.
With a hollow brass ball, moreover, he produced the effects obtained
by Mr. Barlow.  Iron was in no way necessary: the only condition of
success was that the rotating body should be of a character to admit
of the formation of currents in its substance: it must, in other
words, be a conductor of electricity.  The higher the conducting
power the more copious were the currents.  He now passes from his
little brass globe to the globe of the earth.  He plays like a
magician with the earth's magnetism.  He sees the invisible lines
along which its magnetic action is exerted, and sweeping his wand
across these lines evokes this new power.  Placing a simple loop of
wire round a magnetic needle he bends its upper portion to the west:
the north pole of the needle immediately swerves to the east: he
bends his loop to the east, and the north pole moves to the west.
Suspending a common bar magnet in a vertical position, he causes it
to spin round its own axis.  Its pole being connected with one end
of a galvanometer wire, and its equator with the other end,
electricity rushes round the galvanometer from the rotating magnet. 
He remarks upon the 'singular independence' of the magnetism and the
body of the magnet which carries it.  The steel behaves as if it
were isolated from its own magnetism.  

And then his thoughts suddenly widen, and he asks himself whether
the rotating earth does not generate induced currents as it turns
round its axis from west to east.  In his experiment with the
twirling magnet the galvanometer wire remained at rest; one portion
of the circuit was in motion relatively to another portion.  But in
the case of the twirling planet the galvanometer wire would
necessarily be carried along with the earth; there would be no
relative motion.  What must be the consequence?  Take the case of a
telegraph wire with its two terminal plates dipped into the earth,
and suppose the wire to lie in the magnetic meridian.  The ground
underneath the wire is influenced like the wire itself by the
earth's rotation; if a current from south to north be generated in
the wire, a similar current from south to north would be generated
in the earth under the wire; these currents would run against the
same terminal plate, and thus neutralise each other.

This inference appears inevitable, but his profound vision perceived
its possible invalidity.  He saw that it was at least possible that
the difference of conducting power between the earth and the wire
might give one an advantage over the other, and that thus a residual
or differential current might be obtained.  He combined wires of
different materials, and caused them to act in opposition to each
other, but found the combination ineffectual.  The more copious flow
in the better conductor was exactly counterbalanced by the
resistance of the worse.  Still, though experiment was thus emphatic,
he would clear his mind of all discomfort by operating on the earth
itself.  He went to the round lake near Kensington Palace, and
stretched 480 feet of copper wire, north and south, over the lake,
causing plates soldered to the wire at its ends to dip into the
water.  The copper wire was severed at the middle, and the severed
ends connected with a galvanometer.  No effect whatever was observed.
But though quiescent water gave no effect, moving water might.
He therefore worked at London Bridge for three days during the ebb
and flow of the tide, but without any satisfactory result.  Still he
urges, 'Theoretically it seems a necessary consequence, that where
water is flowing there electric currents should be formed.  If a line
be imagined passing from Dover to Calais through the sea, and
returning through the land, beneath the water, to Dover, it traces
out a circuit of conducting matter one part of which, when the water
moves up or down the channel, is cutting the magnetic curves of the
earth, whilst the other is relatively at rest....  There is every
reason to believe that currents do run in the general direction of
the circuit described, either one way or the other, according as the
passage of the waters is up or down the channel.' This was written
before the submarine cable was thought of, and he once informed me
that actual observation upon that cable had been found to be in
accordance with his theoretic deduction.[1]

Three years subsequent to the publication of these researches--
that is to say, on January 29, 1835--Faraday read before the Royal
Society a paper 'On the influence by induction of an electric
current upon itself.'  A shock and spark of a peculiar character had
been observed by a young man named William Jenkin, who must have
been a youth of some scientific promise, but who, as Faraday once
informed me, was dissuaded by his own father from having anything to
do with science.  The investigation of the fact noticed by Mr. Jenkin
led Faraday to the discovery of the extra current, or the current
induced in the primary wire itself at the moments of making and
breaking contact, the phenomena of which he described and
illustrated in the beautiful and exhaustive paper referred to.

Seven-and-thirty years have passed since the discovery of
magneto-electricity; but, if we except the extra current, until
quite recently nothing of moment was added to the subject.  Faraday
entertained the opinion that the discoverer of a great law or
principle had a right to the 'spoils'--this was his term--arising
from its illustration; and guided by the principle he had discovered,
his wonderful mind, aided by his wonderful ten fingers, overran in a
single autumn this vast domain, and hardly left behind him the shred
of a fact to be gathered by his successors.

And here the question may arise in some minds, What is the use of it
all?  The answer is, that if man's intellectual nature thirsts for
knowledge, then knowledge is useful because it satisfies this
thirst.  If you demand practical ends, you must, I think, expand your
definition of the term practical, and make it include all that
elevates and enlightens the intellect, as well as all that ministers
to the bodily health and comfort of men.  Still, if needed, an answer
of another kind might be given to the question 'What is its use?'
As far as electricity has been applied for medical purposes, it has
been almost exclusively Faraday's electricity.  You have noticed
those lines of wire which cross the streets of London.  It is
Faraday's currents that speed from place to place through these
wires.  Approaching the point of Dungeness, the mariner sees an
unusually brilliant light, and from the noble phares of La Heve the
same light flashes across the sea.  These are Faraday's sparks
exalted by suitable machinery to sunlike splendour.  At the present
moment the Board of Trade and the Brethren of the Trinity House, as
well as the Commissioners of Northern Lights, are contemplating the
introduction of the Magneto-electric Light at numerous points upon
our coasts; and future generations will be able to refer to those
guiding stars in answer to the question.  What has been the practical
use of the labours of Faraday?  But I would again emphatically say,
that his work needs no such justification, and that if he had
allowed his vision to be disturbed by considerations regarding the
practical use of his discoveries, those discoveries would never have
been made by him. 'I have rather,' he writes in 1831, 'been desirous
of discovering new facts and new relations dependent on
magneto-electric induction, than of exalting the force of those
already obtained; being assured that the latter would find their
full development hereafter.'

In 1817, when lecturing before a private society in London on the
element chlorine, Faraday thus expressed himself with reference to
this question of utility.  'Before leaving this subject, I will point
out the history of this substance, as an answer to those who are in
the habit of saying to every new fact.  "What is its use?"
Dr. Franklin says to such, "What is the use of an infant?"  The answer
of the experimentalist is, "Endeavour to make it useful."  When Scheele
discovered this substance, it appeared to have no use; it was in its
infancy and useless state, but having grown up to maturity, witness
its powers, and see what endeavours to make it useful have done.'

Footnote to Chapter 3

[1] I am indebted to a friend for the following exquisite morsel:--
'A short time after the publication of Faraday's first researches in
magneto-electricity, he attended the meeting of the British
Association at Oxford, in 1832.  On this occasion he was requested
by some of the authorities to repeat the celebrated experiment of
eliciting a spark from a magnet, employing for this purpose the
large magnet in the Ashmolean Museum.  To this he consented, and a
large party assembled to witness the experiments, which, I need not
say, were perfectly successful.  Whilst he was repeating them a
dignitary of the University entered the room, and addressing himself
to Professor Daniell, who was standing near Faraday, inquired what
was going on.  The Professor explained to him as popularly as
possible this striking result of Faraday's great discovery.
The Dean listened with attention and looked earnestly at the brilliant
spark, but a moment after he assumed a serious countenance and shook
his head; "I am sorry for it," said he, as he walked away; in the
middle of the room he stopped for a moment and repeated, "I am sorry
for it:" then walking towards the door, when the handle was in his
hand he turned round and said, "Indeed I am sorry for it; it is
putting new arms into the hands of the incendiary."  This occurred a
short time after the papers had been filled with the doings of the
hayrick burners.  An erroneous statement of what fell from the
Dean's mouth was printed at the time in one of the Oxford papers. 
He is there wrongly stated to have said, "It is putting new arms
into the hands of the infidel."'


Chapter 4.

Points of Character.

A point highly illustrative of the character of Faraday now comes into
view.  He gave an account of his discovery of Magneto-electricity
in a letter to his friend M. Hachette, of Paris, who communicated
the letter to the Academy of Sciences.  The letter was translated
and published; and immediately afterwards two distinguished Italian
philosophers took up the subject, made numerous experiments, and
published their results before the complete memoirs of Faraday had
met the public eye.  This evidently irritated him.  He reprinted the
paper of the learned Italians in the 'Philosophical Magazine,'
accompanied by sharp critical notes from himself.  He also wrote a
letter dated Dec. 1, 1832, to Gay Lussac, who was then one of the
editors of the 'Annales de Chimie,' in which he analysed the results
of the Italian philosophers, pointing out their errors, and defending
himself from what he regarded as imputations on his character.
The style of this letter is unexceptionable, for Faraday could not
write otherwise than as a gentleman; but the letter shows that had he
willed it he could have hit hard.  We have heard much of Faraday's
gentleness and sweetness and tenderness.  It is all true, but it is
very incomplete.  You cannot resolve a powerful nature into these
elements, and Faraday's character would have been less admirable
than it was had it not embraced forces and tendencies to which the
silky adjectives 'gentle' and 'tender' would by no means apply. 
Underneath his sweetness and gentleness was the heat of a volcano. 
He was a man of excitable and fiery nature; but through high
self-discipline he had converted the fire into a central glow and
motive power of life, instead of permitting it to waste itself in
useless passion.  'He that is slow to anger,' saith the sage,
'is greater than the mighty, and he that ruleth his own spirit than
he that taketh a city.'  Faraday was not slow to anger, but he
completely ruled his own spirit, and thus, though he took no cities,
he captivated all hearts.

As already intimated, Faraday had contributed many of his minor
papers--including his first analysis of caustic lime--to the
'Quarterly Journal of Science.' In 1832, he collected those papers
and others together in a small octavo volume, labelled them, and
prefaced them thus:--

'PAPERS, NOTES, NOTICES, &c., &c.,
published in octavo, up to 1832.
M. Faraday.'

'Papers of mine, published in octavo, in the "Quarterly Journal of
Science," and elsewhere, since the time that Sir H. Davy encouraged
me to write the analysis of caustic lime.  

'Some, I think (at this date), are good; others moderate; and some
bad.  But I have put all into the volume, because of the utility
they have been of to me--and none more than the bad--in pointing out
to me in future, or rather, after times, the faults it became me to
watch and to avoid.

'As I never looked over one of my papers a year after it was written
without believing both in philosophy and manner it could have been
much better done, I still hope the collection may be of great use to
me.  

 'M. Faraday.
 'Aug.  18, 1832.'

'None more than the bad!' This is a bit of Faraday's innermost nature;
and as I read these words I am almost constrained to retract what I
have said regarding the fire and excitability of his character.
But is he not all the more admirable, through his ability to tone
down and subdue that fire and that excitability, so as to render
himself able to write thus as a little child? I once took the liberty
of censuring the conclusion of a letter of his to the Dean of
St. Paul's.  He subscribed himself 'humbly yours,' and I objected to
the adverb.  'Well, but, Tyndall,' he said, 'I am humble; and still
it would be a great mistake to think that I am not also proud.'
This duality ran through his character.  A democrat in his defiance
of all authority which unfairly limited his freedom of thought,
and still ready to stoop in reverence to all that was really worthy
of reverence, in the customs of the world or the characters of men.

And here, as well as elsewhere, may be introduced a letter which
bears upon this question of self-control, written long years
subsequent to the period at which we have now arrived.  I had been
at Glasgow in 1855, at a meeting of the British Association.  On a
certain day, I communicated a paper to the physical section, which
was followed by a brisk discussion.  Men of great distinction took
part in it, the late Dr. Whewell among the number, and it waxed warm
on both sides.  I was by no means content with this discussion; and
least of all, with my own part in it.  This discontent affected me
for some days, during which I wrote to Faraday, giving him no
details, but expressing, in a general way, my dissatisfaction.
I give the following extract from his reply:--

'Sydenham, Oct.  6, 1855.

'My Dear Tyndall,--These great meetings, of which I think very well
altogether, advance science chiefly by bringing scientific men
together and making them to know and be friends with each other;
and I am sorry when that is not the effect in every part of their
course.  I know nothing except from what you tell me, for I have not
yet looked at the reports of the proceedings; but let me, as an old
man, who ought by this time to have profited by experience, say that
when I was younger I found I often misinterpreted the intentions of
people, and found they did not mean what at the time I supposed they
meant; and, further, that as a general rule, it was better to be a
little dull of apprehension where phrases seemed to imply pique,
and quick in perception when, on the contrary, they seemed to imply
kindly feeling.  The real truth never fails ultimately to appear;
and opposing parties, if wrong, are sooner convinced when replied to
forbearingly, than when overwhelmed.  All I mean to say is, that it
is better to be blind to the results of partisanship, and quick to
see good will.  One has more happiness in oneself in endeavouring to
follow the things that make for peace.  You can hardly imagine how
often I have been heated in private when opposed, as I have thought,
unjustly and superciliously, and yet I have striven, and succeeded,
I hope, in keeping down replies of the like kind. And I know I have
never lost by it.  I would not say all this to you did I not esteem
you as a true philosopher and friend.[1]

'Yours, very truly,
'M.  Faraday.'


Footnote to Chapter 4

[1] Faraday would have been rejoiced to learn that, during its last
meeting at Dundee, the British Association illustrated in a striking
manner the function which he here describes as its principal one. 
In my own case, a brotherly welcome was everywhere manifested.
In fact, the differences of really honourable and sane men are never
beyond healing.


Chapter 5.

 Identity of electricities; first researches on electro-chemistry.

I have already once used the word 'discomfort' in reference to the
occasional state of Faraday's mind when experimenting.  It was to
him a discomfort to reason upon data which admitted of doubt.
He hated what he called 'doubtful knowledge,' and ever tended either
to transfer it into the region of undoubtful knowledge, or of certain
and definite ignorance. Pretence of all kinds, whether in life or in
philosophy, was hateful to him. He wished to know the reality of our
nescience as well as of our science. 'Be one thing or the other,'
he seemed to say to an unproved hypothesis; 'come out as a solid truth,
or disappear as a convicted lie.' After making the great discovery
which I have attempted to describe, a doubt seemed to beset him as
regards the identity of electricities.  'Is it right,' he seemed to ask,
'to call this agency which I have discovered electricity at all?
Are there perfectly conclusive grounds for believing that the
electricity of the machine, the pile, the gymnotus and torpedo,
magneto-electricity and thermo-electricity, are merely different
manifestations of one and the same agent?'  To answer this question
to his own satisfaction he formally reviewed the knowledge of that day.
He added to it new experiments of his own, and finally decided
in favour of the 'Identity of Electricities.'  His paper upon this
subject was read before the Royal Society on January 10 and 17, 1833.

After he had proved to his own satisfaction the identity of
electricities, he tried to compare them quantitatively together. 
The terms quantity and intensity, which Faraday constantly used,
need a word of explanation here. He might charge a single Leyden jar
by twenty turns of his machine, or he might charge a battery of ten
jars by the same number of turns.  The quantity in both cases would
be sensibly the same, but the intensity of the single jar would be
the greatest, for here the electricity would be less diffused.
Faraday first satisfied himself that the needle of his galvanometer
was caused to swing through the same arc by the same quantity of
machine electricity, whether it was condensed in a small battery or
diffused over a large one.  Thus the electricity developed by thirty
turns of his machine produced, under very variable conditions of
battery surface, the same deflection.  Hence he inferred the
possibility of comparing, as regards quantity, electricities which
differ greatly from each other in intensity. His object now is to
compare frictional with voltaic electricity.  Moistening bibulous
paper with the iodide of potassium--a favourite test of his--and
subjecting it to the action of machine electricity, he decomposed
the iodide, and formed a brown spot where the iodine was liberated. 
Then he immersed two wires, one of zinc, the other of platinum, each
1/13th of an inch in diameter, to a depth of 5/8ths of an inch in
acidulated water during eight beats of his watch, or 3/20ths of a
second; and found that the needle of his galvanometer swung through
the same arc, and coloured his moistened paper to the same extent,
as thirty turns of his large electrical machine. Twenty-eight turns
of the machine produced an effect distinctly less than that produced
by his two wires.  Now, the quantity of water decomposed by the
wires in this experiment totally eluded observation; it was
immeasurably small; and still that amount of decomposition involved
the development of a quantity of electric force which, if applied in
a proper form, would kill a rat, and no man would like to bear it.

In his subsequent researches 'On the absolute Quantity of
Electricity associated with the Particles or Atoms of matter,'
he endeavours to give an idea of the amount of electrical force
involved in the decomposition of a single grain of water.  He is
almost afraid to mention it, for he estimates it at 800,000
discharges of his large Leyden battery.  This, if concentrated in a
single discharge, would be equal to a very great flash of lightning;
while the chemical action of a single grain of water on four grains
of zinc would yield electricity equal in quantity to a powerful
thunderstorm.  Thus his mind rises from the minute to the vast,
expanding involuntarily from the smallest laboratory fact till it
embraces the largest and grandest natural phenomena.[1]

In reality, however, he is at this time only clearing his way,
and he continues laboriously to clear it for some time afterwards.
He is digging the shaft, guided by that instinct towards the mineral
lode which was to him a rod of divination.  'Er riecht die Wahrheit,'
said the lamented Kohlrausch, an eminent German, once in my hearing:--
'He smells the truth.' His eyes are now steadily fixed on this
wonderful voltaic current, and he must learn more of its mode of
transmission.  

On May 23, 1833, he read a paper before the Royal Society 'On a new
Law of Electric Conduction.'  He found that, though the current
passed through water, it did not pass through ice:--why not, since
they are one and the same substance? Some years subsequently he
answered this question by saying that the liquid condition enables
the molecule of water to turn round so as to place itself in the
proper line of polarization, while the rigidity of the solid
condition prevents this arrangement.  This polar arrangement must
precede decomposition, and decomposition is an accompaniment of
conduction. He then passed on to other substances; to oxides and
chlorides, and iodides, and salts, and sulphurets, and found them
all insulators when solid, and conductors when fused.  In all cases,
moreover, except one--and this exception he thought might be
apparent only--he found the passage of the current across the fused
compound to be accompanied by its decomposition.  Is then the act of
decomposition essential to the act of conduction in these bodies?
Even recently this question was warmly contested.  Faraday was very
cautious latterly in expressing himself upon this subject; but as a
matter of fact he held that an infinitesimal quantity of electricity
might pass through a compound liquid without producing its
decomposition.  De la Rive, who has been a great worker on the
chemical phenomena of the pile, is very emphatic on the other side. 
Experiment, according to him and others, establishes in the most
conclusive manner that no trace of electricity can pass through a
liquid compound without producing its equivalent decomposition.[2]

Faraday has now got fairly entangled amid the chemical phenomena of
the pile, and here his previous training under Davy must have been
of the most important service to him.  Why, he asks, should
decomposition thus take place?--what force is it that wrenches the
locked constituents of these compounds asunder?  On the 20th of June,
1833, he read a paper before the Royal Society 'On Electro-chemical
Decomposition,' in which he seeks to answer these questions.
The notion had been entertained that the poles, as they are called,
of the decomposing cell, or in other words the surfaces by which the
current enters and quits the liquid, exercised electric attractions
upon the constituents of the liquid and tore them asunder.  Faraday
combats this notion with extreme vigour.  Litmus reveals, as you
know, the action of an acid by turning red, turmeric reveals the
action of an alkali by turning brown.  Sulphate of soda, you know,
is a salt compounded of the alkali soda and sulphuric acid.
The voltaic current passing through a solution of this salt so
decomposes it, that sulphuric acid appears at one pole of the
decomposing cell and alkali at the other.  Faraday steeped a piece
of litmus paper and a piece of turmeric paper in a solution of
sulphate of soda: placing each of them upon a separate plate of
glass, he connected them together by means of a string moistened
with the same solution.  He then attached one of them to the
positive conductor of an electric machine, and the other to the
gas-pipes of this building.  These he called his 'discharging train.'
On turning the machine the electricity passed from paper to paper
through the string, which might be varied in length from a few
inches to seventy feet without changing the result.  The first paper
was reddened, declaring the presence of sulphuric acid; the second
was browned, declaring the presence of the alkali soda.
The dissolved salt, therefore, arranged in this fashion, was decomposed
by the machine, exactly as it would have been by the voltaic
current.  When instead of using the positive conductor he used the
negative, the positions of the acid and alkali were reversed.
Thus he satisfied himself that chemical decomposition by the machine
is obedient to the laws which rule decomposition by the pile.  

And now he gradually abolishes those so-called poles, to the
attraction of which electric decomposition had been ascribed.
He connected a piece of turmeric paper moistened with the sulphate
of soda with the positive conductor of his machine; then he placed a
metallic point in connection with his discharging train opposite the
moist paper, so that the electricity should discharge through the
air towards the point.  The turning of the machine caused the
corners of the piece of turmeric paper opposite to the point to turn
brown, thus declaring the presence of alkali.  He changed the
turmeric for litmus paper, and placed it, not in connection with his
conductor, but with his discharging train, a metallic point
connected with the conductor being fixed at a couple of inches from
the paper; on turning the machine, acid was liberated at the edges
and corners of the litmus.  He then placed a series of pointed
pieces of paper, each separate piece being composed of two halves,
one of litmus and the other of turmeric paper, and all moistened
with sulphate of soda, in the line of the current from the machine. 
The pieces of paper were separated from each other by spaces of air. 
The machine was turned; and it was always found that at the point
where the electricity entered the paper, litmus was reddened, and at
the point where it quitted the paper, turmeric was browned.  'Here,'
he urges, 'the poles are entirely abandoned, but we have still
electrochemical decomposition.' It is evident to him that instead of
being attracted by the poles, the bodies separated are ejected by
the current.  The effects thus obtained with poles of air he also
succeeded in obtaining with poles of water.  The advance in
Faraday's own ideas made at this time is indicated by the word
'ejected.' He afterwards reiterates this view: the evolved
substances are expelled from the decomposing body, and 'not drawn
out by an attraction.

Having abolished this idea of polar attraction, he proceeds to
enunciate and develop a theory of his own.  He refers to Davy's
celebrated Bakerian Lecture, given in 1806, which he says 'is almost
entirely occupied in the consideration of electrochemical
decompositions.' The facts recorded in that lecture Faraday regards
as of the utmost value.  But 'the mode of action by which the
effects take place is stated very generally; so generally, indeed, 
that probably a dozen precise schemes of electrochemical action
might be drawn up, differing essentially from each other, yet all
agreeing with the statement there given.'

It appears to me that these words might with justice be applied to
Faraday's own researches at this time.  They furnish us with results
of permanent value; but little help can be found in the theory
advanced to account for them.  It would, perhaps, be more correct to
say that the theory itself is hardly presentable in any tangible
form to the intellect.  Faraday looks, and rightly looks, into the
heart of the decomposing body itself; he sees, and rightly sees,
active within it the forces which produce the decomposition, and he
rejects, and rightly rejects, the notion of external attraction;
but beyond the hypothesis of decompositions and recompositions,
enunciated and developed by Grothuss and Davy, he does not, I think,
help us to any definite conception as to how the force reaches the
decomposing mass and acts within it.  Nor, indeed, can this be done,
until we know the true physical process which underlies what we call
an electric current.

Faraday conceives of that current as 'an axis of power having
contrary forces exactly equal in amount in opposite directions';
but this definition, though much quoted and circulated, teaches us
nothing regarding the current. An 'axis' here can only mean a
direction; and what we want to be able to conceive of is, not the
axis along which the power acts, but the nature and mode of action
of the power itself.  He objects to the vagueness of De la Rive;
but the fact is, that both he and De la Rive labour under the same
difficulty.  Neither wishes to commit himself to the notion of a
current compounded of two electricities flowing in two opposite
directions: but the time had not come, nor is it yet come, for the
displacement of this provisional fiction by the true mechanical
conception.  Still, however indistinct the theoretic notions of
Faraday at this time may be, the facts which are rising before him
and around him are leading him gradually, but surely, to results of
incalculable importance in relation to the philosophy of the voltaic
pile.

He had always some great object of research in view, but in the
pursuit of it he frequently alighted on facts of collateral interest,
to examine which he sometimes turned aside from his direct course. 
Thus we find the series of his researches on electrochemical
decomposition interrupted by an inquiry into 'the power of metals
and other solids, to induce the combination of gaseous bodies.'  This
inquiry, which was received by the Royal Society on Nov. 30, 1833,
though not so important as those which precede and follow it,
illustrates throughout his strength as an experimenter.  The power
of spongy platinum to cause the combination of oxygen and hydrogen
had been discovered by Dobereiner in 1823, and had been applied by
him in the construction of his well-known philosophic lamp.  It was
shown subsequently by Dulong and Thenard that even a platinum wire,
when perfectly cleansed, may be raised to incandescence by its
action on a jet of cold hydrogen.

In his experiments on the decomposition of water, Faraday found that
the positive platinum plate of the decomposing cell possessed in an
extraordinary degree the power of causing oxygen and hydrogen to
combine.  He traced the cause of this to the perfect cleanness of
the positive plate. Against it was liberated oxygen, which, with the
powerful affinity of the 'nascent state,' swept away all impurity
from the surface against which it was liberated.  The bubbles of gas
liberated on one of the platinum plates or wires of a decomposing
cell are always much smaller, and they rise in much more rapid
succession than those from the other.  Knowing that oxygen is
sixteen times heavier than hydrogen, I have more than once concluded,
and, I fear, led others into the error of concluding, that the smaller
and more quickly rising bubbles must belong to the lighter gas.
The thing appeared so obvious that I did not give myself the trouble
of looking at the battery, which would at once have told me the nature
of the gas.  But Faraday would never have been satisfied with a
deduction if he could have reduced it to a fact.  And he has taught
me that the fact here is the direct reverse of what I supposed it to
be.  The small bubbles are oxygen, and their smallness is due to the
perfect cleanness of the surface on which they are liberated.
The hydrogen adhering to the other electrode swells into large bubbles,
which rise in much slower succession; but when the current is reversed,
the hydrogen is liberated upon the cleansed wire, and then its bubbles
also become small.

Footnotes to Chapter 5

[1] Buff finds the quantity of electricity associated with one
milligramme of hydrogen in water to be equal to 45,480 charges of a
Leyden jar, with a height of 480 millimetres, and a diameter of 160
millimetres.  Weber and Kohlrausch have calculated that, if the
quantity of electricity associated with one milligramme of hydrogen
in water were diffused over a cloud at a height of 1000 metres above
the earth, it would exert upon an equal quantity of the opposite
electricity at the earth's surface an attractive force of 2,268,000
kilogrammes.  (Electrolytische Maasbestimmungen, 1856, p. 262.) 

[2] Faraday, sa Vie et ses Travaux, p. 20.


Chapter 6.

 Laws of electro-chemical decomposition.

In our conceptions and reasonings regarding the forces of nature,
we perpetually make use of symbols which, when they possess a high
representative value, we dignify with the name of theories.  Thus,
prompted by certain analogies, we ascribe electrical phenomena to
the action of a peculiar fluid, sometimes flowing, sometimes at
rest.  Such conceptions have their advantages and their
disadvantages; they afford peaceful lodging to the intellect for a
time, but they also circumscribe it, and by-and-by, when the mind
has grown too large for its lodging, it often finds difficulty in
breaking down the walls of what has become its prison instead of its
home.[1]

No man ever felt this tyranny of symbols more deeply than Faraday,
and no man was ever more assiduous than he to liberate himself from
them, and the terms which suggested them.  Calling Dr. Whewell to
his aid in 1833, he endeavoured to displace by others all terms
tainted by a foregone conclusion. His paper on Electro-chemical
Decomposition, received by the Royal Society on January 9, 1834,
opens with the proposal of a new terminology.  He would avoid the
word 'current' if he could.[2] He does abandon the word 'poles' as
applied to the ends of a decomposing cell, because it suggests the
idea of attraction, substituting for it the perfectly natural term
Electrodes.  He applied the term Electrolyte to every substance
which can be decomposed by the current, and the act of decomposition
he called Electrolysis.  All these terms have become current in
science.  He called the positive electrode the Anode, and the
negative one the Cathode, but these terms, though frequently used,
have not enjoyed the same currency as the others.  The terms Anion
and Cation, which he applied to the constituents of the decomposed
electrolyte, and the term Ion, which included both anions and
cations, are still less frequently employed.

Faraday now passes from terminology to research; he sees the
necessity of quantitative determinations, and seeks to supply
himself with a measure of voltaic electricity.  This he finds in the
quantity of water decomposed by the current.  He tests this measure
in all possible ways, to assure himself that no error can arise from
its employment.  He places in the course of one and the same current
a series of cells with electrodes of different sizes, some of them
plates of platinum, others merely platinum wires, and collects the
gas liberated on each distinct pair of electrodes.  He finds the
quantity of gas to be the same for all.  Thus he concludes that when
the same quantity of electricity is caused to pass through a series
of cells containing acidulated water, the electro-chemical action is
independent of the size of the electrodes.[3]  He next proves that
variations in intensity do not interfere with this equality of
action.  Whether his battery is charged with strong acid or with
weak; whether it consists of five pairs or of fifty pairs; in short,
whatever be its source, when the same current is sent through his
series of cells the same amount of decomposition takes place in all. 
He next assures himself that the strength or weakness of his dilute
acid does not interfere with this law.  Sending the same current
through a series of cells containing mixtures of sulphuric acid and
water of different strengths, he finds, however the proportion of
acid to water might vary, the same amount of gas to be collected in
all the cells.  A crowd of facts of this character forced upon
Faraday's mind the conclusion that the amount of electro-chemical
decomposition depends, not upon the size of the electrodes, not upon
the intensity of the current, not upon the strength of the solution,
but solely upon the quantity of electricity which passes through the
cell.  The quantity of electricity he concludes is proportional to
the amount of chemical action.  On this law Faraday based the
construction of his celebrated Voltameter, or Measure of Voltaic
electricity.

But before he can apply this measure he must clear his ground of
numerous possible sources of error.  The decomposition of his
acidulated water is certainly a direct result of the current; but as
the varied and important researches of MM.  Becquerel, De la Rive,
and others had shown, there are also secondary actions which may
materially interfere with and complicate the pure action of the
current.  These actions may occur in two ways: either the liberated
ion may seize upon the electrode against which it is set free,
forming a chemical compound with that electrode; or it may seize
upon the substance of the electrolyte itself, and thus introduce
into the circuit chemical actions over and above those due to the
current.  Faraday subjected these secondary actions to an exhaustive
examination.  Instructed by his experiments, and rendered competent
by them to distinguish between primary and secondary results, he
proceeds to establish the doctrine of 'Definite Electro-chemical
Decomposition.'

Into the same circuit he introduced his voltameter, which consisted
of a graduated tube filled with acidulated water and provided with
platinum plates for the decomposition of the water, and also a cell
containing chloride of tin.  Experiments already referred to had
taught him that this substance, though an insulator when solid, is a
conductor when fused, the passage of the current being always
accompanied by the decomposition of the chloride.  He wished to
ascertain what relation this decomposition bore to that of the water
in his voltameter.

Completing his circuit, he permitted the current to continue until
'a reasonable quantity of gas' was collected in the voltameter.  The
circuit was then broken, and the quantity of tin liberated compared
with the quantity of gas.  The weight of the former was 3.2 grains,
that of the latter 0.49742 of a grain.  Oxygen, as you know, unites
with hydrogen in the proportion of 8 to 1, to form water.  Calling
the equivalent, or as it is sometimes called, the atomic weight of
hydrogen 1, that of oxygen is 8; that of water is consequently 8 + 1
or 9.  Now if the quantity of water decomposed in Faraday's
experiment be represented by the number 9, or in other words by the
equivalent of water, then the quantity of tin liberated from the
fused chloride is found by an easy calculation to be 57.9, which is
almost exactly the chemical equivalent of tin.  Thus both the water
and the chloride were broken up in proportions expressed by their
respective equivalents.  The amount of electric force which wrenched
asunder the constituents of the molecule of water was competent,
and neither more nor less than competent, to wrench asunder the
constituents of the molecules of the chloride of tin. The fact is
typical.  With the indications of his voltameter he compared the
decompositions of other substances, both singly and in series.
He submitted his conclusions to numberless tests.  He purposely
introduced secondary actions.  He endeavoured to hamper the
fulfilment of those laws which it was the intense desire of his mind
to see established.  But from all these difficulties emerged the
golden truth, that under every variety of circumstances the
decompositions of the voltaic current are as definite in their
character as those chemical combinations which gave birth to the
atomic theory.  This law of Electro-chemical Decomposition ranks,
in point of importance, with that of Definite Combining Proportions
in chemistry.

Footnotes to Chapter 6

[1] I copy these words from the printed abstract of a Friday
evening lecture, given by myself, because they remind me of
Faraday's voice, responding to the utterance by an emphatic 'hear!
hear!'--Proceedings of the Royal Institution, vol. ii. p. 132.

[2] In 1838 he expresses himself thus:--'The word current is so
expressive in common language that when applied in the consideration
of electrical phenomena, we can hardly divest it sufficiently of its
meaning, or prevent our minds from being prejudiced by it.'--
Exp. Resear., vol. i. p. 515. ($ 1617.)

[3] This conclusion needs qualification.  Faraday overlooked the
part played by ozone.


Chapter 7.

 Origin of power in the voltaic pile.

In one of the public areas of the town of Como stands a statue with
no inscription on its pedestal, save that of a single name, 'Volta.'
The bearer of that name occupies a place for ever memorable in the
history of science. To him we owe the discovery of the voltaic pile,
to which for a brief interval we must now turn our attention.

The objects of scientific thought being the passionless laws and
phenomena of external nature, one might suppose that their
investigation and discussion would be completely withdrawn from the
region of the feelings, and pursued by the cold dry light of the
intellect alone.  This, however, is not always the case.
Man carries his heart with him into all his works.  You cannot
separate the moral and emotional from the intellectual; and thus it
is that the discussion of a point of science may rise to the heat of
a battle-field. The fight between the rival optical theories of
Emission and Undulation was of this fierce character; and scarcely
less fierce for many years was the contest as to the origin and
maintenance of the power of the voltaic pile. Volta himself supposed
it to reside in the Contact of different metals.  Here was exerted
his 'Electro-motive force,' which tore the combined electricities
asunder and drove them as currents in opposite directions.
To render the circulation of the current possible, it was necessary
to connect the metals by a moist conductor; for when any two metals
were connected by a third, their relation to each other was such
that a complete neutralisation of the electric motion was the result.
Volta's theory of metallic contact was so clear, so beautiful, and
apparently so complete, that the best intellects of Europe accepted
it as the expression of natural law.

Volta himself knew nothing of the chemical phenomena of the pile;
but as soon as these became known, suggestions and intimations
appeared that chemical action, and not metallic contact, might be
the real source of voltaic electricity.  This idea was expressed by
Fabroni in Italy, and by Wollaston in England.  It was developed and
maintained by those 'admirable electricians,' Becquerel, of Paris,
and De la Rive, of Geneva.  The Contact Theory, on the other hand,
received its chief development and illustration in Germany.
It was long the scientific creed of the great chemists and natural
philosophers of that country, and to the present hour there may be
some of them unable to liberate themselves from the fascination of
their first-love.

After the researches which I have endeavoured to place before you,
it was impossible for Faraday to avoid taking a side in this
controversy.  He did so in a paper 'On the Electricity of the
Voltaic Pile,' received by the Royal Society on the 7th of April,
1834.  His position in the controversy might have been predicted. 
He saw chemical effects going hand in hand with electrical effects,
the one being proportional to the other; and, in the paper now
before us, he proved that when the former was excluded, the latter
were sought for in vain.  He produced a current without metallic
contact; he discovered liquids which, though competent to transmit
the feeblest currents--competent therefore to allow the electricity
of contact to flow through them if it were able to form a
current--were absolutely powerless when chemically inactive.

One of the very few experimental mistakes of Faraday occurred in
this investigation.  He thought that with a single voltaic cell he
had obtained the spark before the metals touched, but he
subsequently discovered his error.  To enable the voltaic spark to
pass through air before the terminals of the battery were united, it
was necessary to exalt the electro-motive force of the battery by
multiplying its elements; but all the elements Faraday possessed
were unequal to the task of urging the spark across the shortest
measurable space of air.  Nor, indeed, could the action of the
battery, the different metals of which were in contact with each
other, decide the point in question.  Still, as regards the identity
of electricities from various sources, it was at that day of great
importance to determine whether or not the voltaic current could
jump, as a spark, across an interval before contact.  Faraday's
friend, Mr. Gassiot, solved this problem.  He erected a battery of
4000 cells, and with it urged a stream of sparks from terminal to
terminal, when separated from each other by a measurable space of air.

The memoir on the 'Electricity of the Voltaic Pile,' published in
1834, appears to have produced but little impression upon the
supporters of the contact theory.  These indeed were men of too
great intellectual weight and insight lightly to take up, or lightly
to abandon a theory.  Faraday therefore resumed the attack in a
paper, communicated to the Royal Society on the 6th of February,
1840.  In this paper he hampered his antagonists by a crowd of
adverse experiments.  He hung difficulty after difficulty about the
neck of the contact theory, until in its efforts to escape from his
assaults it so changed its character as to become a thing totally
different from the theory proposed by Volta.  The more persistently
it was defended, however, the more clearly did it show itself to be
a congeries of devices, bearing the stamp of dialectic skill rather
than of natural truth.

In conclusion, Faraday brought to bear upon it an argument which,
had its full weight and purport been understood at the time, would
have instantly decided the controversy.  'The contact theory,'
he urged, 'assumed that a force which is able to overcome powerful
resistance, as for instance that of the conductors, good or bad,
through which the current passes, and that again of the electrolytic
action where bodies are decomposed by it, can arise out of nothing;
that, without any change in the acting matter, or the consumption of
any generating force, a current shall be produced which shall go on
for ever against a constant resistance, or only be stopped, as in
the voltaic trough, by the ruins which its exertion has heaped up in
its own course.  This would indeed be a creation of power, and is
like no other force in nature.  We have many processes by which the
form of the power may be so changed, that an apparent conversion of
one into the other takes place.  So we can change chemical force
into the electric current, or the current into chemical force.
The beautiful experiments of Seebeck and Peltier show the convertibility
of heat and electricity; and others by Oersted and myself show the
convertibility of electricity and magnetism.  But in no case, not
even in those of the Gymnotus and Torpedo, is there a pure creation
or a production of power without a corresponding exhaustion of
something to supply it.'

These words were published more than two years before either Mayer
printed his brief but celebrated essay on the Forces of Inorganic
Nature, or Mr. Joule published his first famous experiments on the
Mechanical Value of Heat.  They illustrate the fact that before any
great scientific principle receives distinct enunciation by
individuals, it dwells more or less clearly in the general
scientific mind.  The intellectual plateau is already high, and our
discoverers are those who, like peaks above the plateau, rise a
little above the general level of thought at the time.

But many years prior even to the foregoing utterance of Faraday,
a similar argument had been employed.  I quote here with equal
pleasure and admiration the following passage written by Dr. Roget
so far back as 1829.  Speaking of the contact theory, he says:--
'If there could exist a power having the property ascribed to it by
the hypothesis, namely, that of giving continual impulse to a fluid
in one constant direction, without being exhausted by its own
action, it would differ essentially from all the known powers in
nature. All the powers and sources of motion with the operation of
which we are acquainted, when producing these peculiar effects, are
expended in the same proportion as those effects are produced; and
hence arises the impossibility of obtaining by their agency a
perpetual effect; or in other words a perpetual motion.  But the
electro-motive force, ascribed by Volta to the metals, when in
contact, is a force which, as long as a free course is allowed to
the electricity it sets in motion, is never expended, and continues
to be excited with undiminished power in the production of a
never-ceasing effect.  Against the truth of such a supposition the
probabilities are all but infinite.'  When this argument, which he
employed independently, had clearly fixed itself in his mind,
Faraday never cared to experiment further on the source of
electricity in the voltaic pile.  The argument appeared to him
'to remove the foundation itself of the contact theory,' and he
afterwards let it crumble down in peace.[1]

Footnote to Chapter 7

[1] To account for the electric current, which was really the core
of the whole discussion, Faraday demonstrated the impotence of the
Contact Theory as then enunciated and defended.  Still, it is
certain that two different metals, when brought into contact, charge
themselves, the one with positive and the other with negative
electricity.  I had the pleasure of going over this ground with
Kohlrausch in 1849, and his experiments left no doubt upon my mind
that the contact electricity of Volta was a reality, though it could
produce no current.  With one of the beautiful instruments devised
by himself, Sir William Thomson has rendered this point capable of
sure and easy demonstration; and he and others now hold what may be
called a contact theory, which, while it takes into account the
action of the metals, also embraces the chemical phenomena of the
circuit.  Helmholtz, I believe, was the first to give the contact
theory this new form, in his celebrated essay, Ueber die Erhaltung
der Kraft, p. 45.
 

Chapter 8.

 Researches on frictional electricity: induction: conduction:
 specific inductive capacity: theory of contiguous particles.

The burst of power which had filled the four preceding years with an
amount of experimental work unparalleled in the history of science
partially subsided in 1835, and the only scientific paper contributed
by Faraday in that year was a comparatively unimportant one, 'On an
improved Form of the Voltaic Battery.'  He brooded for a time: his
experiments on electrolysis had long filled his mind; he looked, as
already stated, into the very heart of the electrolyte, endeavouring
to render the play of its atoms visible to his mental eye.  He had
no doubt that in this case what is called 'the electric current' was
propagated from particle to particle of the electrolyte; he accepted
the doctrine of decomposition and recomposition which, according to
Grothuss and Davy, ran from electrode to electrode.  And the thought
impressed him more and more that ordinary electric induction was
also transmitted and sustained by the action of 'contiguous
particles.'

His first great paper on frictional electricity was sent to the
Royal Society on November 30, 1837.  We here find him face to face
with an idea which beset his mind throughout his whole subsequent
life,--the idea of action at a distance.  It perplexed and
bewildered him.  In his attempts to get rid of this perplexity, he
was often unconsciously rebelling against the limitations of the
intellect itself.  He loved to quote Newton upon this point; over
and over again he introduces his memorable words, 'That gravity
should be innate, inherent, and essential to matter, so that one
body may act upon another at a distance through a vacuum and without
the mediation of anything else, by and through which this action and
force may be conveyed from one to another, is to me so great an
absurdity, that I believe no man who has in philosophical matters a
competent faculty of thinking, can ever fall into it.  Gravity must
be caused by an agent acting constantly according to certain laws;
but whether this agent be material or immaterial, I have left to the
consideration of my readers.'[1]

Faraday does not see the same difficulty in his contiguous particles.
And yet, by transferring the conception from masses to particles,
we simply lessen size and distance, but we do not alter the quality
of the conception.  Whatever difficulty the mind experiences in
conceiving of action at sensible distances, besets it also when it
attempts to conceive of action at insensible distances.  Still the
investigation of the point whether electric and magnetic effects
were wrought out through the intervention of contiguous particles or
not, had a physical interest altogether apart from the metaphysical
difficulty.  Faraday grapples with the subject experimentally.
By simple intuition he sees that action at a distance must be exerted
in straight lines.  Gravity, he knows, will not turn a corner, but
exerts its pull along a right line; hence his aim and effort to
ascertain whether electric action ever takes place in curved lines. 
This once proved, it would follow that the action is carried on by
means of a medium surrounding the electrified bodies.  His experiments
in 1837 reduced, in his opinion, this point of demonstration.
He then found that he could electrify, by induction, an insulated
sphere placed completely in the shadow of a body which screened it
from direct action.  He pictured the lines of electric force bending
round the edges of the screen, and reuniting on the other side of it;
and he proved that in many cases the augmentation of the distance
between his insulated sphere and the inducing body, instead of
lessening, increased the charge of the sphere.  This he ascribed to
the coalescence of the lines of electric force at some distance
behind the screen.

Faraday's theoretic views on this subject have not received general
acceptance, but they drove him to experiment, and experiment with
him was always prolific of results.  By suitable arrangements he
placed a metallic sphere in the middle of a large hollow sphere,
leaving a space of something more than half an inch between them. 
The interior sphere was insulated, the external one uninsulated.
To the former he communicated a definite charge of electricity.
It acted by induction upon the concave surface of the latter, and he
examined how this act of induction was effected by placing insulators
of various kinds between the two spheres.  He tried gases, liquids,
and solids, but the solids alone gave him positive results.
He constructed two instruments of the foregoing description, equal in
size and similar in form. The interior sphere of each communicated
with the external air by a brass stem ending in a knob.
The apparatus was virtually a Leyden jar, the two coatings of which
were the two spheres, with a thick and variable insulator between
them.  The amount of charge in each jar was determined by bringing a
proof-plane into contact with its knob and measuring by a torsion
balance the charge taken away.  He first charged one of his
instruments, and then dividing the charge with the other, found that
when air intervened in both cases the charge was equally divided. 
But when shellac, sulphur, or spermaceti was interposed between the
two spheres of one jar, while air occupied this interval in the
other, then he found that the instrument occupied by the 'solid
dielectric' takes more than half the original charge.  A portion of
the charge was absorbed by the dielectric itself.  The electricity
took time to penetrate the dielectric.  Immediately after the
discharge of the apparatus, no trace of electricity was found upon
its knob. But after a time electricity was found there, the charge
having gradually returned from the dielectric in which it had been
lodged.  Different insulators possess this power of permitting the
charge to enter them in different degrees.  Faraday figured their
particles as polarized, and he concluded that the force of induction
is propagated from particle to particle of the dielectric from the
inner sphere to the outer one.  This power of propagation possessed
by insulators he called their 'Specific Inductive Capacity.'

Faraday visualizes with the utmost clearness the state of his
contiguous particles; one after another they become charged, each
succeeding particle depending for its charge upon its predecessor. 
And now he seeks to break down the wall of partition between
conductors and insulators.  'Can we not,' he says, 'by a gradual
chain of association carry up discharge from its occurrence in air
through spermaceti and water, to solutions, and then on to chlorides,
oxides, and metals, without any essential change in its character?'
Even copper, he urges, offers a resistance to the transmission of
electricity.  The action of its particles differs from those of an
insulator only in degree.  They are charged like the particles of
the insulator, but they discharge with greater ease and rapidity;
and this rapidity of molecular discharge is what we call conduction. 
Conduction then is always preceded by atomic induction; and when,
through some quality of the body which Faraday does not define, the
atomic discharge is rendered slow and difficult, conduction passes
into insulation.

Though they are often obscure, a fine vein of philosophic thought
runs through those investigations.  The mind of the philosopher
dwells amid those agencies which underlie the visible phenomena of
Induction and Conduction; and he tries by the strong light of his
imagination to see the very molecules of his dielectrics.  It would,
however, be easy to criticise these researches, easy to show the
looseness, and sometimes the inaccuracy, of the phraseology
employed; but this critical spirit will get little good out of
Faraday.  Rather let those who ponder his works seek to realise the
object he set before him, not permitting his occasional vagueness to
interfere with their appreciation of his speculations.  We may see
the ripples, and eddies, and vortices of a flowing stream, without
being able to resolve all these motions into their constituent
elements; and so it sometimes strikes me that Faraday clearly saw
the play of fluids and ethers and atoms, though his previous
training did not enable him to resolve what he saw into its
constituents, or describe it in a manner satisfactory to a mind
versed in mechanics.  And then again occur, I confess, dark sayings,
difficult to be understood, which disturb my confidence in this
conclusion.  It must, however, always be remembered that he works at
the very boundaries of our knowledge, and that his mind habitually
dwells in the 'boundless contiguity of shade' by which that
knowledge is surrounded.  

In the researches now under review the ratio of speculation and
reasoning to experiment is far higher than in any of Faraday's
previous works.  Amid much that is entangled and dark we have
flashes of wondrous insight and utterances which seem less the
product of reasoning than of revelation.  I will confine myself here
to one example of this divining power.  By his most ingenious device
of a rapidly rotating mirror, Wheatstone had proved that electricity
required time to pass through a wire, the current reaching the
middle of the wire later than its two ends.  'If,' says Faraday,
'the two ends of the wire in Professor Wheatstone's experiments were
immediately connected with two large insulated metallic surfaces
exposed to the air, so that the primary act of induction, after
making the contact for discharge, might be in part removed from the
internal portion of the wire at the first instance, and disposed for
the moment on its surface jointly with the air and surrounding
conductors, then I venture to anticipate that the middle spark would
be more retarded than before.  And if those two plates were the
inner and outer coatings of a large jar or Leyden battery, then the
retardation of the spark would be much greater.' This was only a
prediction, for the experiment was not made.[2]  Sixteen years
subsequently, however, the proper conditions came into play, and
Faraday was able to show that the observations of Werner Siemens,
and Latimer Clark, on subterraneous and submarine wires were
illustrations, on a grand scale, of the principle which he had
enunciated in 1838.  The wires and the surrounding water act as a
Leyden jar, and the retardation of the current predicted by Faraday
manifests itself in every message sent by such cables.

The meaning of Faraday in these memoirs on Induction and Conduction
is, as I have said, by no means always clear; and the difficulty
will be most felt by those who are best trained in ordinary
theoretic conceptions.  He does not know the reader's needs, and he
therefore does not meet them.  For instance he speaks over and over
again of the impossibility of charging a body with one electricity,
though the impossibility is by no means evident.  The key to the
difficulty is this.  He looks upon every insulated conductor as the
inner coating of a Leyden jar.  An insulated sphere in the middle of
a room is to his mind such a coating; the walls are the outer coating,
while the air between both is the insulator, across which the charge
acts by induction. Without this reaction of the walls upon the
sphere you could no more, according to Faraday, charge it with
electricity than you could charge a Leyden jar, if its outer coating
were removed.  Distance with him is immaterial.  His strength as a
generalizer enables him to dissolve the idea of magnitude; and if
you abolish the walls of the room--even the earth itself--he would
make the sun and planets the outer coating of his jar.  I dare not
contend that Faraday in these memoirs made all his theoretic
positions good.  But a pure vein of philosophy runs through these
writings; while his experiments and reasonings on the forms and
phenomena of electrical discharge are of imperishable importance.

Footnotes to Chapter 8

[1] Newton's third letter to Bentley.

[2] Had Sir Charles Wheatstone been induced to resume his measurements,
varying the substances through which, and the conditions under which,
the current is propagated, he might have rendered great service to
science, both theoretic and experimental.


Chapter 9.

 Rest needed--visit to Switzerland.

The last of these memoirs was dated from the Royal Institution in
June, 1838.  It concludes the first volume of his 'Experimental
Researches on Electricity.'  In 1840, as already stated, he made his
final assault on the Contact Theory, from which it never recovered.[1]
He was now feeling the effects of the mental strain to which he had
been subjected for so many years.  During these years he repeatedly
broke down.  His wife alone witnessed the extent of his prostration,
and to her loving care we, and the world, are indebted for the
enjoyment of his presence here so long.  He found occasional relief
in a theatre.  He frequently quitted London and went to Brighton and
elsewhere, always choosing a situation which commanded a view of the
sea, or of some other pleasant horizon, where he could sit and gaze
and feel the gradual revival of the faith that

  'Nature never did betray 
   The heart that loved her.'

But very often for some days after his removal to the country, he
would be unable to do more than sit at a window and look out upon
the sea and sky.

In 1841, his state became more serious than it had ever been before. 
A published letter to Mr. Richard Taylor, dated March 11, 1843,
contains an allusion to his previous condition.  'You are aware,'
he says, 'that considerations regarding health have prevented me
from working or reading on science for the last two years.'  This,
at one period or another of their lives, seems to be the fate of
most great investigators.  They do not know the limits of their
constitutional strength until they have transgressed them. It is,
perhaps, right that they should transgress them, in order to
ascertain where they lie.  Faraday, however, though he went far
towards it, did not push his transgression beyond his power of
restitution.  In 1841 Mrs. Faraday and he went to Switzerland, under
the affectionate charge of her brother, Mr. George Barnard, the artist.
This time of suffering throws fresh light upon his character.
I have said that sweetness and gentleness were not its only
constituents; that he was also fiery and strong.  At the time now
referred to, his fire was low and his strength distilled away; but
the residue of his life was neither irritability nor discontent.
He was unfit to mingle in society, for conversation was a pain to him;
but let us observe the great Man-child when alone.  He is at the
village of Interlaken, enjoying Jungfrau sunsets, and at times
watching the Swiss nailers making their nails.  He keeps a little
journal, in which he describes the process of nailmaking, and
incidentally throws a luminous beam upon himself.

'August 2, 1841.--Clout nailmaking goes on here rather considerably,
and is a very neat and pretty operation to observe.  I love a
smith's shop and anything relating to smithery.  My father was a
smith.'

From Interlaken he went to the Falls of the Giessbach, on the
pleasant lake of Brientz.  And here we have him watching the shoot
of the cataract down its series of precipices.  It is shattered into
foam at the base of each, and tossed by its own recoil as water-dust
through the air.  The sun is at his back, shining on the drifting
spray, and he thus describes and muses on what he sees:--

'August 12, 1841.--To-day every fall was foaming from the abundance
of water, and the current of wind brought down by it was in some
places too strong to stand against.  The sun shone brightly, and the
rainbows seen from various points were very beautiful.  One at the
bottom of a fine but furious fall was very pleasant,--there it
remained motionless, whilst the gusts and clouds of spray swept
furiously across its place and were dashed against the rock.
It looked like a spirit strong in faith and steadfast in the midst
of the storm of passions sweeping across it, and though it might
fade and revive, still it held on to the rock as in hope and giving
hope. And the very drops, which in the whirlwind of their fury
seemed as if they would carry all away, were made to revive it and
give it greater beauty.'

Footnote to Chapter 9

[1] See note, p. 77.


Chapter 10.

 Magnetization of light.

But we must quit the man and go on to the discoverer: we shall
return for a brief space to his company by-and-by.  Carry your
thoughts back to his last experiments, and see him endeavouring to
prove that induction is due to the action of contiguous particles. 
He knew that polarized light was a most subtle and delicate
investigator of molecular condition.  He used it in 1834 in
exploring his electrolytes, and he tried it in 1838 upon his
dielectrics. At that time he coated two opposite faces of a glass
cube with tinfoil, connected one coating with his powerful electric
machine and the other with the earth, and examined by polarized
light the condition of the glass when thus subjected to strong
electric influence.  He failed to obtain any effect; still he was
persuaded an action existed, and required only suitable means to
call it forth.

After his return from Switzerland he was beset by these thoughts;
they were more inspired than logical: but he resorted to magnets and
proved his inspiration true.  His dislike of 'doubtful knowledge'
and his efforts to liberate his mind from the thraldom of hypotheses
have been already referred to.  Still this rebel against theory was
incessantly theorising himself.  His principal researches are all
connected by an undercurrent of speculation. Theoretic ideas were
the very sap of his intellect--the source from which all his
strength as an experimenter was derived.  While once sauntering with
him through the Crystal Palace, at Sydenham, I asked him what
directed his attention to the magnetization of light.  It was his
theoretic notions.  He had certain views regarding the unity and
convertibility of natural forces; certain ideas regarding the
vibrations of light and their relations to the lines of magnetic
force; these views and ideas drove him to investigation.  And so it
must always be: the great experimentalist must ever be the habitual
theorist, whether or not he gives to his theories formal
enunciation.  

Faraday, you have been informed, endeavoured to improve the
manufacture of glass for optical purposes.  But though he produced a
heavy glass of great refractive power, its value to optics did not
repay him for the pains and labour bestowed on it.  Now, however,
we reach a result established by means of this same heavy glass,
which made ample amends for all.

In November, 1845, he announced his discovery of the 'Magnetization
of Light and the Illumination of the Lines of Magnetic Force.'
This title provoked comment at the time, and caused misapprehension.
He therefore added an explanatory note; but the note left his meaning
as entangled as before.  In fact Faraday had notions regarding the
magnetization of light which were peculiar to himself, and
untranslatable into the scientific language of the time.  Probably
no other philosopher of his day would have employed the phrases just
quoted as appropriate to the discovery announced in 1845.
But Faraday was more than a philosopher; he was a prophet, and often
wrought by an inspiration to be understood by sympathy alone.
The prophetic element in his character occasionally coloured,
and even injured, the utterance of the man of science; but
subtracting that element, though you might have conferred on him
intellectual symmetry, you would have destroyed his motive force.

But let us pass from the label of this casket to the jewel it contains.
'I have long,' he says, 'held an opinion, almost amounting to
conviction, in common, I believe, with many other lovers of natural
knowledge, that the various forms under which the forces of matter
are made manifest have one common origin; in other words, are so
directly related and mutually dependent, that they are convertible,
as it were, into one another, and possess equivalents of power in
their action....  This strong persuasion,' he adds, 'extended to the
powers of light.' And then he examines the action of magnets upon
light.  From conversation with him and Anderson, I should infer that
the labour preceding this discovery was very great.  The world knows
little of the toil of the discoverer.  It sees the climber jubilant
on the mountain top, but does not know the labour expended in
reaching it. Probably hundreds of experiments had been made on
transparent crystals before he thought of testing his heavy glass. 
Here is his own clear and simple description of the result of his
first experiment with this substance:--'A piece of this glass, about
two inches square, and 0.5 of an inch thick, having flat and
polished edges, was placed as a diamagnetic[1] between the poles
(not as yet magnetized by the electric current), so that the
polarized ray should pass through its length; the glass acted as
air, water, or any other transparent substance would do; and if the
eye-piece were previously turned into such a position that the
polarized ray was extinguished, or rather the image produced by it
rendered invisible, then the introduction of the glass made no
alteration in this respect.  In this state of circumstances, the
force of the electro-magnet was developed by sending an electric
current through its coils, and immediately the image of the
lamp-flame became visible and continued so as long as the
arrangement continued magnetic.  On stopping the electric current,
and so causing the magnetic force to cease, the light instantly
disappeared.  These phenomena could be renewed at pleasure, at any
instant of time, and upon any occasion, showing a perfect dependence
of cause and effect.'

In a beam of ordinary light the particles of the luminiferous ether
vibrate in all directions perpendicular to the line of progression;
by the act of polarization, performed here by Faraday, all
oscillations but those parallel to a certain plane are eliminated. 
When the plane of vibration of the polarizer coincides with that of
the analyzer, a portion of the beam passes through both; but when
these two planes are at right angles to each other, the beam is
extinguished.  If by any means, while the polarizer and analyzer
remain thus crossed, the plane of vibration of the polarized beam
between them could be changed, then the light would be, in part at
least, transmitted.  In Faraday's experiment this was accomplished. 
His magnet turned the plane of polarization of the beam through a
certain angle, and thus enabled it to get through the analyzer;
so that 'the magnetization of light and the illumination of the
magnetic lines of force' becomes, when expressed in the language of
modern theory, the rotation of the plane of polarization.

To him, as to all true philosophers, the main value of a fact was
its position and suggestiveness in the general sequence of
scientific truth. Hence, having established the existence of a
phenomenon, his habit was to look at it from all possible points of
view, and to develop its relationship to other phenomena.  He proved
that the direction of the rotation depends upon the polarity of his
magnet; being reversed when the magnetic poles are reversed.
He showed that when a polarized ray passed through his heavy glass
in a direction parallel to the magnetic lines of force, the rotation
is a maximum, and that when the direction of the ray is at right
angles to the lines of force, there is no rotation at all.  He also
proved that the amount of the rotation is proportional to the length
of the diamagnetic through which the ray passes.  He operated with
liquids and solutions.  Of aqueous solutions he tried 150 and more,
and found the power in all of them.  He then examined gases; but
here all his efforts to produce any sensible action upon the
polarized beam were ineffectual.  He then passed from magnets to
currents, enclosing bars of heavy glass, and tubes containing
liquids and aqueous solutions within an electro-magnetic helix.
A current sent through the helix caused the plane of polarization to
rotate, and always in the direction of the current.  The rotation
was reversed when the current was reversed.  In the case of magnets,
he observed a gradual, though quick, ascent of the transmitted beam
from a state of darkness to its maximum brilliancy, when the magnet
was excited.  In the case of currents, the beam attained at once its
maximum.  This he showed to be due to the time required by the iron
of the electro-magnet to assume its full magnetic power, which time
vanishes when a current, without iron, is employed.  'In this
experiment,' he says, 'we may, I think, justly say that a ray of
light is electrified, and the electric forces illuminated.' In the
helix, as with the magnets, he submitted air to magnetic influence
'carefully and anxiously,' but could not discover any trace of
action on the polarized ray.

Many substances possess the power of turning the plane of polarization
without the intervention of magnetism.  Oil of turpentine and quartz
are examples; but Faraday showed that, while in one direction,
that is, across the lines of magnetic force, his rotation is zero,
augmenting gradually from this until it attains its maximum, when
the direction of the ray is parallel to the lines of force; in the
oil of turpentine the rotation is independent of the direction of
the ray.  But he showed that a still more profound distinction
exists between the magnetic rotation and the natural one.  I will
try to explain how.  Suppose a tube with glass ends containing oil
of turpentine to be placed north and south.  Fixing the eye at the
south end of the tube, let a polarized beam be sent through it from
the north.  To the observer in this position the rotation of the
plane of polarization, by the turpentine, is right-handed.  Let the
eye be placed at the north end of the tube, and a beam be sent
through it from the south; the rotation is still right-handed.
Not so, however, when a bar of heavy glass is subjected to the
action of an electric current.  In this case if, in the first
position of the eye, the rotation be right-handed, in the second
position it is left-handed.  These considerations make it manifest
that if a polarized beam, after having passed through the oil of
turpentine in its natural state, could by any means be reflected
back through the liquid, the rotation impressed upon the direct beam
would be exactly neutralized by that impressed upon the reflected
one.  Not so with the induced magnetic effect. Here it is manifest
that the rotation would be doubled by the act of reflection.
Hence Faraday concludes that the particles of the oil of turpentine
which rotate by virtue of their natural force, and those which
rotate in virtue of the induced force, cannot be in the same
condition.  The same remark applies to all bodies which possess a
natural power of rotating the plane of polarization.

And then he proceeded with exquisite skill and insight to take
advantage of this conclusion.  He silvered the ends of his piece of
heavy glass, leaving, however, a narrow portion parallel to two
edges diagonally opposed to each other unsilvered.  He then sent his
beam through this uncovered portion, and by suitably inclining his
glass caused the beam within it to reach his eye first direct, and
then after two, four, and six reflections.  These corresponded to
the passage of the ray once, three times, five times, and seven
times through the glass.  He thus established with numerical
accuracy the exact proportionality of the rotation to the distance
traversed by the polarized beam.  Thus in one series of experiments
where the rotation required by the direct beam was 12degrees, that
acquired by three passages through the glass was 36degrees, while that
acquired by five passages was 60degrees.  But even when this method of
magnifying was applied, he failed with various solid substances to
obtain any effect; and in the case of air, though he employed to the
utmost the power which these repeated reflections placed in his
hands, he failed to produce the slightest sensible rotation.

These failures of Faraday to obtain the effect with gases seem to
indicate the true seat of the phenomenon.  The luminiferous ether
surrounds and is influenced by the ultimate particles of matter. 
The symmetry of the one involves that of the other.  Thus, if the
molecules of a crystal be perfectly symmetrical round any line
through the crystal, we may safely conclude that a ray will pass
along this line as through ordinary glass.  It will not be doubly
refracted.  From the symmetry of the liquid figures, known to be
produced in the planes of freezing, when radiant heat is sent
through ice, we may safely infer symmetry of aggregation, and hence
conclude that the line perpendicular to the planes of freezing is a
line of no double refraction; that it is, in fact, the optic axis of
the crystal.  The same remark applies to the line joining the
opposite blunt angles of a crystal of Iceland spar.  The arrangement
of the molecules round this line being symmetrical, the condition of
the ether depending upon these molecules shares their symmetry; and
there is, therefore, no reason why the wavelength should alter with
the alteration of the azimuth round this line.  Annealed glass has
its molecules symmetrically arranged round every line that can be
drawn through it; hence it is not doubly refractive.  But let the
substance be either squeezed or strained in one direction, the
molecular symmetry, and with it the symmetry of the ether, is
immediately destroyed and the glass becomes doubly refractive. 
Unequal heating produces the same effect.  Thus mechanical strains
reveal themselves by optical effects; and there is little doubt that
in Faraday's experiment it is the magnetic strain that produces the
rotation of the plane of polarization.[2]

Footnotes to Chapter 10

[1] 'By a diamagnetic,' says Faraday, 'I mean a body through which
lines of magnetic force are passing,  and which does not by their
action assume the usual magnetic state of iron or loadstone.'
Faraday subsequently used this term in a different sense from that
here given, as will immediately appear.

[2] The power of double refraction conferred on the centre of a
glass rod, when it is caused to sound the fundamental note due to
its longitudinal vibration, and the absence of the same power in the
case of vibrating air (enclosed in a glass organ-pipe), seems to be
analogous to the presence and absence of Faraday's effect in the
same two substances.  

Faraday never, to my knowledge, attempted to give, even in
conversation, a picture of the molecular condition of his heavy
glass when subjected to magnetic influence.  In a mathematical
investigation of the subject, published in the Proceedings of the
Royal Society for 1856, Sir William Thomson arrives at the
conclusion that the 'diamagnetic' is in a state of molecular
rotation.


Chapter 11.

 Discovery of diamagnetism--researches on magne-crystallic action.

Faraday's next great step in discovery was announced in a memoir on
the 'Magnetic Condition of all matter,' communicated to the Royal
Society on December 18, 1845.  One great source of his success was
the employment of extraordinary power.  As already stated, he never
accepted a negative answer to an experiment until he had brought to
bear upon it all the force at his command.  He had over and over
again tried steel magnets and ordinary electro-magnets on various
substances, but without detecting anything different from the
ordinary attraction exhibited by a few of them.  Stronger coercion,
however, developed a new action.  Before the pole of an electro-magnet,
he suspended a fragment of his famous heavy glass; and observed that
when the magnet was powerfully excited the glass fairly retreated
from the pole.  It was a clear case of magnetic repulsion.  He then
suspended a bar of the glass between two poles; the bar retreated
when the poles were excited, and set its length equatorially or at
right angles to the line joining them.  When an ordinary magnetic
body was similarly suspended, it always set axially, that is, from
pole to pole.  

Faraday called those bodies which were repelled by the poles of a
magnet, diamagnetic bodies; using this term in a sense different
from that in which he employed it in his memoir on the magnetization
of light.  The term magnetic he reserved for bodies which exhibited
the ordinary attraction.  He afterwards employed the term magnetic
to cover the whole phenomena of attraction and repulsion, and used
the word paramagnetic to designate such magnetic action as is
exhibited by iron.

Isolated observations by Brugmanns, Becquerel, Le Baillif, Saigy,
and Seebeck had indicated the existence of a repulsive force
exercised by the magnet on two or three substances; but these
observations, which were unknown to Faraday, had been permitted to
remain without extension or examination.  Having laid hold of the
fact of repulsion, Faraday immediately expanded and multiplied it. 
He subjected bodies of the most varied qualities to the action of
his magnet:--mineral salts, acids, alkalis, ethers, alcohols,
aqueous solutions, glass, phosphorus, resins, oils, essences,
vegetable and animal tissues, and found them all amenable to
magnetic influence.  No known solid or liquid proved insensible to
the magnetic power when developed in sufficient strength.  All the
tissues of the human body, the blood--though it contains iron--
included, were proved to be diamagnetic.  So that if you could
suspend a man between the poles of a magnet, his extremities would
retreat from the poles until his length became equatorial.

Soon after he had commenced his researches on diamagnetism, Faraday
noticed a remarkable phenomenon which first crossed my own path in
the following way: In the year 1849, while working in the cabinet of
my friend, Professor Knoblauch, of Marburg, I suspended a small
copper coin between the poles of an electro-magnet.  On exciting the
magnet, the coin moved towards the poles and then suddenly stopped,
as if it had struck against a cushion.  On breaking the circuit, the
coin was repelled, the revulsion being so violent as to cause it to
spin several times round its axis of suspension.  A Silber-groschen
similarly suspended exhibited the same deportment.  For a moment I
thought this a new discovery; but on looking over the literature of
the subject, it appeared that Faraday had observed, multiplied, and
explained the same effect during his researches on diamagnetism. 
His explanation was based upon his own great discovery of
magneto-electric currents.  The effect is a most singular one.
A weight of several pounds of copper may be set spinning between the
electro-magnetic poles; the excitement of the magnet instantly stops
the rotation.  Though nothing is apparent to the eye, the copper,
if moved in the excited magnetic field, appears to move through a
viscous fluid; while, when a flat piece of the metal is caused to
pass to and fro like a saw between the poles, the sawing of the
magnetic field resembles the cutting through of cheese or butter.[1] 
This virtual friction of the magnetic field is so strong, that copper,
by its rapid rotation between the poles, might probably be fused. 
We may easily dismiss this experiment by saying that the heat is due
to the electric currents excited in the copper.  But so long as we
are unable to reply to the question, 'What is an electric current?'
the explanation is only provisional.  For my own part, I look with
profound interest and hope on the strange action here referred to.

Faraday's thoughts ran intuitively into experimental combinations,
so that subjects whose capacity for experimental treatment would, to
ordinary minds, seem to be exhausted in a moment, were shown by him
to be all but inexhaustible.  He has now an object in view, the
first step towards which is the proof that the principle of
Archimedes is true of magnetism.  He forms magnetic solutions of
various degrees of strength, places them between the poles of his
magnet, and suspends in the solutions various magnetic bodies.
He proves that when the solution is stronger than the body plunged in
it, the body, though magnetic, is repelled; and when an elongated
piece of it is surrounded by the solution, it sets, like a
diamagnetic body, equatorially between the excited poles.  The same
body when suspended in a solution of weaker magnetic power than
itself, is attracted as a whole, while an elongated portion of it
sets axially.  

And now theoretic questions rush in upon him.  Is this new force a
true repulsion, or is it merely a differential attraction?  Might not
the apparent repulsion of diamagnetic bodies be really due to the
greater attraction of the medium by which they are surrounded?
He tries the rarefaction of air, but finds the effect insensible.
He is averse to ascribing a capacity of attraction to space, or to
any hypothetical medium supposed to fill space.  He therefore
inclines, but still with caution, to the opinion that the action of
a magnet upon bismuth is a true and absolute repulsion, and not
merely the result of differential attraction.  And then he clearly
states a theoretic view sufficient to account for the phenomena. 
'Theoretically,' he says, 'an explanation of the movements of the
diamagnetic bodies, and all the dynamic phenomena consequent upon
the action of magnets upon them, might be offered in the supposition
that magnetic induction caused in them a contrary state to that
which it produced in ordinary matter.'  That is to say, while in
ordinary magnetic influence the exciting pole excites adjacent to
itself the contrary magnetism, in diamagnetic bodies the adjacent
magnetism is the same as that of the exciting pole.  This theory of
reversed polarity, however, does not appear to have ever laid deep
hold of Faraday's mind; and his own experiments failed to give any
evidence of its truth.  He therefore subsequently abandoned it, and
maintained the non-polarity of the diamagnetic force.  

He then entered a new, though related field of inquiry.  Having
dealt with the metals and their compounds, and having classified all
of them that came within the range of his observation under the two
heads magnetic and diamagnetic, he began the investigation of the
phenomena presented by crystals when subjected to magnetic power. 
This action of crystals had been in part theoretically predicted by
Poisson,[2] and actually discovered by Plucker, whose beautiful
results, at the period which we have now reached, profoundly
interested all scientific men.  Faraday had been frequently puzzled
by the deportment of bismuth, a highly crystalline metal.  Sometimes
elongated masses of the substance refused to set equatorially,
sometimes they set persistently oblique, and sometimes even, like a
magnetic body, from pole to pole.

'The effect,' he says, 'occurs at a single pole; and it is then
striking to observe a long piece of a substance so diamagnetic as
bismuth repelled, and yet at the same moment set round with force,
axially, or end on, as a piece of magnetic substance would do.'
The effect perplexed him; and in his efforts to release himself from
this perplexity, no feature of this new manifestation of force
escaped his attention.  His experiments are described in a memoir
communicated to the Royal Society on December 7, 1848.

I have worked long myself at magne-crystallic action, amid all the
light of Faraday's and Plucker's researches.  The papers now before
me were objects of daily and nightly study with me eighteen or
nineteen years ago; but even now, though their perusal is but the
last of a series of repetitions, they astonish me.  Every
circumstance connected with the subject; every shade of deportment;
every variation in the energy of the action; almost every
application which could possibly be made of magnetism to bring out
in detail the character of this new force, is minutely described. 
The field is swept clean, and hardly anything experimental is left
for the gleaner.  The phenomena, he concludes, are altogether
different from those of magnetism or diamagnetism: they would appear,
in fact, to present to us 'a new force, or a new form of force,
in the molecules of matter,' which, for convenience sake, he designates
by a new word, as 'the magne-crystallic force.'

He looks at the crystal acted upon by the magnet.  From its mass he
passes, in idea, to its atoms, and he asks himself whether the power
which can thus seize upon the crystalline molecules, after they have
been fixed in their proper positions by crystallizing force, may not,
when they are free, be able to determine their arrangement?
He, therefore, liberates the atoms by fusing the bismuth.  He places
the fused substance between the poles of an electro-magnet,
powerfully excited; but he fails to detect any action.  I think it
cannot be doubted that an action is exerted here, that a true cause
comes into play; but its magnitude is not such as sensibly to
interfere with the force of crystallization, which, in comparison
with the diamagnetic force, is enormous.  'Perhaps,' adds Faraday,
'if a longer time were allowed, and a permanent magnet used, a
better result might be obtained.  I had built many hopes upon the
process.' This expression, and his writings abound in such,
illustrates what has been already said regarding his experiments
being suggested and guided by his theoretic conceptions.  His mind
was full of hopes and hypotheses, but he always brought them to an
experimental test. The record of his planned and executed experiments
would, I doubt not, show a high ratio of hopes disappointed to hopes
fulfilled; but every case of fulfilment abolished all memory of
defeat; disappointment was swallowed up in victory.  

After the description of the general character of this new force,
Faraday states with the emphasis here reproduced its mode of action:
'The law of action appears to be that the line or axis of
MAGNE-CRYSTALLIC force (being the resultant of the action of all the
molecules) tends to place itself parallel, or as a tangent, to the
magnetic curve, or line of magnetic force, passing through the place
where the crystal is situated.' The magne-crystallic force,
moreover, appears to him 'to be clearly distinguished from the
magnetic or diamagnetic forces, in that it causes neither approach
nor recession, consisting not in attraction or repulsion, but in
giving a certain determinate position to the mass under its
influence.' And then he goes on 'very carefully to examine and prove
the conclusion that there was no connection of the force with
attractive or repulsive influences.' With the most refined ingenuity
he shows that, under certain circumstances, the magne-crystallic
force can cause the centre of gravity of a highly magnetic body to
retreat from the poles, and the centre of gravity of a highly
diamagnetic body to approach them.  His experiments root his mind
more and more firmly in the conclusion that 'neither attraction nor
repulsion causes the set, or governs the final position' of the
crystal in the magnetic field.  That the force which does so is
therefore 'distinct in its character and effects from the magnetic
and diamagnetic forms of force.  On the other hand,' he continues,
'it has a most manifest relation to the crystalline structure of
bismuth and other bodies, and therefore to the power by which their
molecules are able to build up the crystalline masses.'

And here follows one of those expressions which characterize the
conceptions of Faraday in regard to force generally:--'It appears to
me impossible to conceive of the results in any other way than by a
mutual reaction of the magnetic force, and the force of the
particles of the crystals upon each other.' He proves that the
action of the force, though thus molecular, is an action at a
distance; he shows that a bismuth crystal can cause a freely
suspended magnetic needle to set parallel to its magne-crystallic
axis.  Few living men are aware of the difficulty of obtaining
results like this, or of the delicacy necessary to their attainment. 
'But though it thus takes up the character of a force acting at a
distance, still it is due to that power of the particles which makes
them cohere in regular order and gives the mass its crystalline
aggregation, which we call at other times the attraction of
aggregation, and so often speak of as acting at insensible distances.'
Thus he broods over this new force, and looks at it from all
possible points of inspection.  Experiment follows experiment,
as thought follows thought.  He will not relinquish the subject as
long as a hope exists of throwing more light upon it.  He knows full
well the anomalous nature of the conclusion to which his experiments
lead him.  But experiment to him is final, and he will not shrink
from the conclusion.  'This force,' he says, 'appears to me to be
very strange and striking in its character.  It is not polar, for
there is no attraction or repulsion.'  And then, as if startled by
his own utterance, he asks--'What is the nature of the mechanical
force which turns the crystal round, and makes it affect a magnet?'... 
'I do not remember,' he continues 'heretofore such a case of force
as the present one, where a body is brought into position only,
without attraction or repulsion.'

Plucker, the celebrated geometer already mentioned, who pursued
experimental physics for many years of his life with singular
devotion and success, visited Faraday in those days, and repeated
before him his beautiful experiments on magneto-optic action. 
Faraday repeated and verified Plucker's observations, and concluded,
what he at first seemed to doubt, that Plucker's results and
magne-crystallic action had the same origin.

At the end of his papers, when he takes a last look along the line
of research, and then turns his eyes to the future, utterances quite
as much emotional as scientific escape from Faraday.  'I cannot,'
he says, at the end of his first paper on magne-crystallic action,
'conclude this series of researches without remarking how rapidly
the knowledge of molecular forces grows upon us, and how strikingly
every investigation tends to develop more and more their importance,
and their extreme attraction as an object of study.  A few years ago
magnetism was to us an occult power, affecting only a few bodies,
now it is found to influence all bodies, and to possess the most
intimate relations with electricity, heat, chemical action, light,
crystallization, and through it, with the forces concerned in
cohesion; and we may, in the present state of things, well feel
urged to continue in our labours, encouraged by the hope of bringing
it into a bond of union with gravity itself.'



Supplementary remarks

A brief space will, perhaps, be granted me here to state the further
progress of an investigation which interested Faraday so much. 
Drawn by the fame of Bunsen as a teacher, in the year 1848 I became
a student in the University of Marburg, in Hesse Cassel.  Bunsen's
behaviour to me was that of a brother as well as that of a teacher,
and it was also my happiness to make the acquaintance and gain the
friendship of Professor Knoblauch, so highly distinguished by his
researches on Radiant Heat.  Plucker's and Faraday's investigations
filled all minds at the time, and towards the end of 1849, Professor
Knoblauch and myself commenced a joint investigation of the entire
question.  Long discipline was necessary to give us due mastery over it.
Employing a method proposed by Dove, we examined the optical
properties of our crystals ourselves; and these optical observations
went hand in hand with our magnetic experiments.  The number of
these experiments was very great, but for a considerable time no
fact of importance was added to those already published.  At length,
however, it was our fortune to meet with various crystals whose
deportment could not be brought under the laws of magne-crystallic
action enunciated by Plucker.  We also discovered instances which
led us to suppose that the magne-crystallic force was by no means
independent, as alleged, of the magnetism or diamagnetism of the
mass of the crystal.  Indeed, the more we worked at the subject, the
more clearly did it appear to us that the deportment of crystals in
the magnetic field was due, not to a force previously unknown, but
to the modification of the known forces of magnetism and
diamagnetism by crystalline aggregation.

An eminent example of magne-crystallic action adduced by Plucker,
and experimented on by Faraday, was Iceland spar.  It is what in
optics is called a negative crystal, and according to the law of
Plucker, the axis of such a crystal was always repelled by a magnet. 
But we showed that it was only necessary to substitute, in whole or
in part, carbonate of iron for carbonate of lime, thus changing the
magnetic but not the optical character of the crystal, to cause the
axis to be attracted.  That the deportment of magnetic crystals is
exactly antithetical to that of diamagnetic crystals isomorphous
with the magnetic ones, was proved to be a general law of action. 
In all cases, the line which in a diamagnetic crystal set equatorially,
always set itself in an isomorphous magnetic crystal axially.
By mechanical compression other bodies were also made to imitate the
Iceland spar.

These and numerous other results bearing upon the question were
published at the time in the 'Philosophical Magazine' and in
'Poggendorff's Annalen'; and the investigation of diamagnetism and
magne-crystallic action was subsequently continued by me in the
laboratory of Professor Magnus of Berlin.  In December, 1851, after
I had quitted Germany, Dr. Bence Jones went to the Prussian capital
to see the celebrated experiments of Du Bois Reymond.  Influenced, I
suppose, by what he there heard, he afterwards invited me to give a
Friday evening discourse at the Royal Institution.  I consented, not
without fear and trembling.  For the Royal Institution was to me a
kind of dragon's den, where tact and strength would be necessary to
save me from destruction.  On February 11, 1853, the discourse was
given, and it ended happily.  I allude to these things, that I may
mention that, though my aim and object in that lecture was to
subvert the notions both of Faraday and Plucker, and to establish in
opposition to their views what I regarded as the truth, it was very
far from producing in Faraday either enmity or anger.  At the
conclusion of the lecture, he quitted his accustomed seat, crossed
the theatre to the corner into which I had shrunk, shook me by the
hand, and brought me back to the table.  Once more, subsequently,
and in connection with a related question, I ventured to differ from
him still more emphatically.  It was done out of trust in the
greatness of his character; nor was the trust misplaced.  He felt my
public dissent from him; and it pained me afterwards to the quick to
think that I had given him even momentary annoyance.  It was,
however, only momentary.  His soul was above all littleness and
proof to all egotism.  He was the same to me afterwards that he had
been before; the very chance expression which led me to conclude
that he felt my dissent being one of kindness and affection.

It required long subsequent effort to subdue the complications of
magne-crystallic action, and to bring under the dominion of
elementary principles the vast mass of facts which the experiments
of Faraday and Plucker had brought to light.  It was proved by
Reich, Edmond Becquerel, and myself, that the condition of
diamagnetic bodies, in virtue of which they were repelled by the
poles of a magnet, was excited in them by those poles; that the
strength of this condition rose and fell with, and was proportional
to, the strength of the acting magnet.  It was not then any property
possessed permanently by the bismuth, and which merely required the
development of magnetism to act upon it, that caused the repulsion;
for then the repulsion would have been simply proportional to the
strength of the influencing magnet, whereas experiment proved it to
augment as the square of the strength.  The capacity to be repelled
was therefore not inherent in the bismuth, but induced.  So far an
identity of action was established between magnetic and diamagnetic
bodies.  After this the deportment of magnetic bodies, 'normal' and
'abnormal'; crystalline, amorphous, and compressed, was compared
with that of crystalline, amorphous, and compressed diamagnetic
bodies; and by a series of experiments, executed in the laboratory
of this Institution, the most complete antithesis was established
between magnetism and diamagnetism.  This antithesis embraced the
quality of polarity,--the theory of reversed polarity, first
propounded by Faraday, being proved to be true.  The discussion of
the question was very brisk.  On the Continent Professor Wilhelm
Weber was the ablest and most successful supporter of the doctrine
of diamagnetic polarity; and it was with an apparatus, devised by
him and constructed under his own superintendence, by Leyser of
Leipzig, that the last demands of the opponents of diamagnetic
polarity were satisfied.  The establishment of this point was
absolutely necessary to the explanation of magne-crystallic action.  

With that admirable instinct which always guided him, Faraday had
seen that it was possible, if not probable, that the diamagnetic
force acts with different degrees of intensity in different
directions, through the mass of a crystal.  In his studies on
electricity, he had sought an experimental reply to the question
whether crystalline bodies had not different specific inductive
capacities in different directions, but he failed to establish any
difference of the kind.  His first attempt to establish differences
of diamagnetic action in different directions through bismuth, was
also a failure; but he must have felt this to be a point of cardinal
importance, for he returned to the subject in 1850, and proved that
bismuth was repelled with different degrees of force in different
directions.  It seemed as if the crystal were compounded of two
diamagnetic bodies of different strengths, the substance being more
strongly repelled across the magne-crystallic axis than along it. 
The same result was obtained independently, and extended to various
other bodies, magnetic as well as diamagnetic, and also to
compressed substances, a little subsequently by myself.  

The law of action in relation to this point is, that in diamagnetic
crystals, the line along which the repulsion is a maximum, sets
equatorially in the magnetic field; while in magnetic crystals the
line along which the attraction is a maximum sets from pole to pole. 
Faraday had said that the magne-crystallic force was neither
attraction nor repulsion.  Thus far he was right.  It was neither
taken singly, but it was both.  By the combination of the doctrine
of diamagnetic polarity with these differential attractions and
repulsions, and by paying due regard to the character of the
magnetic field, every fact brought to light in the domain of
magne-crystallic action received complete explanation.  The most
perplexing of those facts were shown to result from the action of
mechanical couples, which the proved polarity both of magnetism and
diamagnetism brought into play.  Indeed the thoroughness with which
the experiments of Faraday were thus explained, is the most striking
possible demonstration of the marvellous precision with which they
were executed.

Footnotes to Chapter 11

[1] See Heat as a Mode of Motion, ninth edition, p. 75.

[2] See Sir Wm. Thomson on Magne-crystallic Action. Phil. Mag., 1851.


Chapter 12.

 Magnetism of flame and gases--atmospheric magnetism

When an experimental result was obtained by Faraday it was instantly
enlarged by his imagination.  I am acquainted with no mind whose
power and suddenness of expansion at the touch of new physical truth
could be ranked with his.  Sometimes I have compared the action of
his experiments on his mind to that of highly combustible matter
thrown into a furnace; every fresh entry of fact was accompanied by
the immediate development of light and heat.  The light, which was
intellectual, enabled him to see far beyond the boundaries of the
fact itself, and the heat, which was emotional, urged him to the
conquest of this newly-revealed domain.  But though the force of his
imagination was enormous, he bridled it like a mighty rider, and
never permitted his intellect to be overthrown.

In virtue of the expansive power which his vivid imagination
conferred upon him, he rose from the smallest beginnings to the
grandest ends.  Having heard from Zantedeschi that Bancalari had
established the magnetism of flame, he repeated the experiments and
augmented the results.  He passed from flames to gases, examining
and revealing their magnetic and diamagnetic powers; and then he
suddenly rose from his bubbles of oxygen and nitrogen to the
atmospheric envelope of the earth itself, and its relations to the
great question of terrestrial magnetism.  The rapidity with which
these ever-augmenting thoughts assumed the form of experiments is
unparalleled. His power in this respect is often best illustrated by
his minor investigations, and, perhaps, by none more strikingly than
by his paper 'On the Diamagnetic Condition of Flame and Gases,'
published as a letter to Mr. Richard Taylor, in the 'Philosophical
Magazine' for December, 1847.  After verifying, varying, and
expanding the results of Bancalari, he submitted to examination
heated air-currents, produced by platinum spirals placed in the
magnetic field, and raised to incandescence by electricity.  He then
examined the magnetic deportment of gases generally.  Almost all of
these gases are invisible; but he must, nevertheless, track them in
their unseen courses.  He could not effect this by mingling smoke
with his gases, for the action of his magnet upon the smoke would
have troubled his conclusions.  He, therefore, 'caught' his gases in
tubes, carried them out of the magnetic field, and made them reveal
themselves at a distance from the magnet.

Immersing one gas in another, he determined their differential
action; results of the utmost beauty being thus arrived at.  Perhaps
the most important are those obtained with atmospheric air and its
two constituents. Oxygen, in various media, was strongly attracted
by the magnet; in coal-gas, for example, it was powerfully magnetic,
whereas nitrogen was diamagnetic. Some of the effects obtained with
oxygen in coal-gas were strikingly beautiful.  When the fumes of
chloride of ammonium (a diamagnetic substance) were mingled with the
oxygen, the cloud of chloride behaved in a most singular manner,--
'The attraction of iron filings,' says Faraday, 'to a magnetic pole
is not more striking than the appearance presented by the oxygen
under these circumstances.'

On observing this deportment the question immediately occurs to him,
--Can we not separate the oxygen of the atmosphere from its nitrogen
by magnetic analysis? It is the perpetual occurrence of such
questions that marks the great experimenter.  The attempt to analyze
atmospheric air by magnetic force proved a failure, like the
previous attempt to influence crystallization by the magnet.
The enormous comparative power of the force of crystallization I
have already assigned as a reason for the incompetence of the magnet
to determine molecular arrangement; in the present instance the
magnetic analysis is opposed by the force of diffusion, which is
also very strong comparatively.  The same remark applies to, and is
illustrated by, another experiment subsequently executed by Faraday. 
Water is diamagnetic, sulphate of iron is strongly magnetic.
He enclosed 'a dilute solution of sulphate of iron in a tube,
and placed the lower end of the tube between the poles of a powerful
horseshoe magnet for days together,' but he could produce
'no concentration of the solution in the part near the magnet.'
Here also the diffusibility of the salt was too powerful for the
force brought against it.  

The experiment last referred to is recorded in a paper presented to
the Royal Society on the 2nd August, 1850, in which he pursues the
investigation of the magnetism of gases.  Newton's observations on
soap-bubbles were often referred to by Faraday.  His delight in a
soap-bubble was like that of a boy, and he often introduced them
into his lectures, causing them, when filled with air, to float on
invisible seas of carbonic acid, and otherwise employing them as a
means of illustration.  He now finds them exceedingly useful in his
experiments on the magnetic condition of gases.  A bubble of air in
a magnetic field occupied by air was unaffected, save through the
feeble repulsion of its envelope.  A bubble of nitrogen, on the
contrary, was repelled from the magnetic axis with a force far
surpassing that of a bubble of air.  The deportment of oxygen in air
'was very impressive, the bubble being pulled inward or towards the
axial line, sharply and suddenly, as if the oxygen were highly
magnetic.'

He next labours to establish the true magnetic zero, a problem not
so easy as might at first sight be imagined.  For the action of the
magnet upon any gas, while surrounded by air or any other gas, can
only be differential; and if the experiment were made in vacuo, the
action of the envelope, in this case necessarily of a certain
thickness, would trouble the result.  While dealing with this
subject, Faraday makes some noteworthy observations regarding space. 
In reference to the Torricellian vacuum, he says, 'Perhaps it is
hardly necessary for me to state that I find both iron and bismuth
in such vacua perfectly obedient to the magnet.  From such
experiments, and also from general observations and knowledge, it
seems manifest that the lines of magnetic force can traverse pure
space, just as gravitating force does, and as statical electrical
forces do, and therefore space has a magnetic relation of its own,
and one that we shall probably find hereafter to be of the utmost
importance in natural phenomena.  But this character of space is not
of the same kind as that which, in relation to matter, we endeavour
to express by the terms magnetic and diamagnetic.  To confuse these
together would be to confound space with matter, and to trouble all
the conceptions by which we endeavour to understand and work out a
progressively clearer view of the mode of action, and the laws of
natural forces.  It would be as if in gravitation or electric forces,
one were to confound the particles acting on each other with the
space across which they are acting, and would, I think, shut the
door to advancement.  Mere space cannot act as matter acts, even
though the utmost latitude be allowed to the hypothesis of an ether;
and admitting that hypothesis, it would be a large additional
assumption to suppose that the lines of magnetic force are
vibrations carried on by it, whilst as yet we have no proof that
time is required for their propagation, or in what respect they may,
in general character, assimilate to or differ from their respective
lines of gravitating, luminiferous, or electric forces.'

Pure space he assumes to be the true magnetic zero, but he pushes
his inquiries to ascertain whether among material substances there
may not be some which resemble space.  If you follow his experiments,
you will soon emerge into the light of his results.  A torsion-beam
was suspended by a skein of cocoon silk; at one end of the beam was
fixed a cross-piece 1 1/2 inch long.  Tubes of exceedingly thin glass,
filled with various gases, and hermetically sealed, were suspended
in pairs from the two ends of the cross-piece.  The position of the
rotating torsion-head was such that the two tubes were at opposite
sides of, and equidistant from, the magnetic axis, that is to say
from the line joining the two closely approximated polar points of
an electro-magnet.  His object was to compare the magnetic action of
the gases in the two tubes.  When one tube was filled with oxygen,
and the  other with nitrogen, on the supervention of the magnetic
force, the oxygen was pulled towards the axis, the nitrogen being
pushed out.  By turning the torsion-head they could be restored to
their primitive position of equidistance, where it is evident the
action of the glass envelopes was annulled.  The amount of torsion
necessary to re-establish equidistance expressed the magnetic
difference of the substances compared.  

And then he compared oxygen with oxygen at different pressures.
One of his tubes contained the gas at the pressure of 30 inches of
mercury, another at a pressure of 15 inches of mercury, a third at a
pressure of 10 inches, while a fourth was exhausted as far as a good
air-pump renders exhaustion possible.  'When the first of these was
compared with the other three, the effect was most striking.'
It was drawn towards the axis when the magnet was excited, the tube
containing the rarer gas being apparently driven away, and the
greater the difference between the densities of the two gases,
the greater was the energy of this action.  

And now observe his mode of reaching a material magnetic zero.
When a bubble of nitrogen was exposed in air in the magnetic field,
on the supervention of the power, the bubble retreated from the magnet. 
A less acute observer would have set nitrogen down as diamagnetic;
but Faraday knew that retreat, in a medium composed in part of oxygen,
might be due to the attraction of the latter gas, instead of to the
repulsion of the gas immersed in it.  But if nitrogen be really
diamagnetic, then a bubble or bulb filled with the dense gas will
overcome one filled with the rarer gas.  From the cross-piece of his
torsion-balance he suspended his bulbs of nitrogen, at equal distances
from the magnetic axis, and found that the rarefaction, or the
condensation of the gas in either of the bulbs had not the slightest
influence.  When the magnetic force was developed, the bulbs
remained in their first position, even when one was filled with
nitrogen, and the other as far as possible exhausted.  Nitrogen,
in fact, acted 'like space itself'; it was neither magnetic nor
diamagnetic.  

He cannot conveniently compare the paramagnetic force of oxygen with
iron, in consequence of the exceeding magnetic intensity of the
latter substance; but he does compare it with the sulphate of iron,
and finds that, bulk for bulk, oxygen is equally magnetic with a
solution of this substance in water 'containing seventeen times the
weight of the oxygen in crystallized proto-sulphate of iron, or 3.4
times its weight of metallic iron in that state of combination.'
By its capability to deflect a fine glass fibre, he finds that the
attraction of this bulb of oxygen, containing only 0.117 of a grain
of the gas, at an average distance of more than an inch from the
magnetic axis, is about equal to the gravitating force of the same
amount of oxygen as expressed by its weight.

These facts could not rest for an instant in the mind of Faraday
without receiving that expansion to which I have already referred. 
'It is hardly necessary,' he writes, 'for me to say here that this
oxygen cannot exist in the atmosphere exerting such a remarkable and
high amount of magnetic force, without having a most important
influence on the disposition of the magnetism of the earth, as a
planet; especially if it be remembered that its magnetic condition
is greatly altered by variations of its density and by variations of
its temperature.  I think I see here the real cause of many of the
variations of that force, which have been, and are now so carefully
watched on different parts of the surface of the globe.  The daily
variation, and the annual variation, both seem likely to come under
it; also very many of the irregular continual variations, which the
photographic process of record renders so beautifully manifest. 
If such expectations be  confirmed, and the influence of the atmosphere
be found able to produce results like these, then we shall probably
find a new relation between the aurora borealis and the magnetism of
the earth, namely, a relation established, more or less, through the
air itself in connection with the space above it; and even magnetic
relations and variations, which are not as yet suspected, may be
suggested and rendered manifest and measurable, in the further
development of what I will venture to call Atmospheric Magnetism.
I may be over-sanguine in these expectations, but as yet I am sustained
in them by the apparent reality, simplicity, and sufficiency of the
cause assumed, as it at present appears to my mind.  As soon as I
have submitted these views to a close consideration, and the test of
accordance with observation, and, where applicable, with experiments
also, I will do myself the honour to bring them before the Royal
Society.' 

Two elaborate memoirs are then devoted to the subject of Atmospheric
Magnetism; the first sent to the Royal Society on the 9th of October,
and the second on the 19th of November, 1850.  In these memoirs he
discusses the effects of heat and cold upon the magnetism of the
air, and the action on the magnetic needle, which must result from
thermal changes.  By the convergence and divergence of the lines of
terrestrial magnetic force, he shows how the distribution of
magnetism, in the earth's atmosphere, is effected.  He applies his
results to the explanation of the Annual and of the Diurnal Variation:
he also considers irregular variations, including the action of
magnetic storms.  He discusses, at length, the observations at
St. Petersburg, Greenwich, Hobarton, St.  Helena, Toronto, and the
Cape of Good Hope; believing that the facts, revealed by his
experiments, furnish the key to the variations observed at all these
places.  

In the year 1851, I had the honour of an interview with Humboldt, in
Berlin, and his parting words to me then were, 'Tell Faraday that I
entirely agree with him, and that he has, in my opinion, completely
explained the variation of the declination.'  Eminent men have since
informed me that Humboldt was hasty in expressing this opinion.  In
fact, Faraday's memoirs on atmospheric magnetism lost much of their
force--perhaps too much--through the important discovery of the
relation of the variation of the declination to the number of the
solar spots.  But I agree with him and M. Edmond Becquerel, who
worked independently at this subject, in thinking, that a body so
magnetic as oxygen, swathing the earth, and subject to variations of
temperature, diurnal and annual, must affect the manifestations of
terrestrial magnetism.[1] The air that stands upon a single square
foot of the earth's surface is, according to Faraday, equivalent in
magnetic force to 8160 lbs. of crystallized protosulphate of iron. 
Such a substance cannot be absolutely neutral as regards the
deportment of the magnetic needle.  But Faraday's writings on this
subject are so voluminous, and the theoretic points are so novel and
intricate, that I shall postpone the complete analysis of these
researches to a time when I can lay hold of them more completely
than my other duties allow me to do now.  

Footnote to Chapter 12

[1] This persuasion has been greatly strengthened by the recent
perusal of a paper by Mr. Baxendell.


Chapter 13.
 
 Speculations: nature of matter: lines of force

The scientific picture of Faraday would not be complete without a
reference to his speculative writings.  On Friday, January 19, 1844,
he opened the weekly evening-meetings of the Royal Institution by a
discourse entitled 'A speculation touching Electric Conduction and
the nature of Matter.'  In this discourse he not only attempts the
overthrow of Dalton's Theory of Atoms, but also the subversion of
all ordinary scientific ideas regarding the nature and relations of
Matter and Force.  He objected to the use of the term atom:--'I have
not yet found a mind,' he says, 'that did habitually separate it
from its accompanying temptations; and there can be no doubt that
the words definite proportions, equivalent, primes, &c., which did
and do fully express all the facts of what is usually called the
atomic theory in chemistry, were dismissed because they were not
expressive enough, and did not say all that was in the mind of him
who used the word atom in their stead.' 

A moment will be granted me to indicate my own view of Faraday's
position here.  The word 'atom' was not used in the stead of
definite proportions, equivalents, or primes.  These terms
represented facts that followed from, but were not equivalent to,
the atomic theory.  Facts cannot satisfy the mind: and the law of
definite combining proportions being once established, the question
'why should combination take place according to that law?' is
inevitable.  Dalton answered this question by the enunciation of the
Atomic Theory, the fundamental idea of which is, in my opinion,
perfectly secure. The objection of Faraday to Dalton might be urged
with the same substantial force against Newton: it might be stated
with regard to the planetary motions that the laws of Kepler
revealed the facts; that the introduction of the principle of
gravitation was an addition to the facts.  But this is the essence
of all theory.  The theory is the backward guess from fact to
principle; the conjecture, or divination regarding something, which
lies behind the facts, and from which they flow in necessary
sequence.  If Dalton's theory, then, account for the definite
proportions observed in the combinations of chemistry, its
justification rests upon the same basis as that of the principle of
gravitation.  All that can in strictness be said in either case is
that the facts occur as if the principle existed.  

The manner in which Faraday himself habitually deals with his
hypotheses is revealed in this lecture.  He incessantly employed
them to gain experimental ends, but he incessantly took them down,
as an architect removes the scaffolding when the edifice is complete.
'I cannot but doubt,' he says, 'that he who as a mere philosopher
has most power of penetrating the secrets of nature, and guessing by
hypothesis at her mode of working, will also be most careful for his
own safe progress and that of others, to distinguish the knowledge
which consists of assumption, by which I mean theory and hypothesis,
from that which is the knowledge of facts and laws.'  Faraday
himself, in fact, was always 'guessing by hypothesis,' and making
theoretic divination the stepping-stone to his experimental results.  

I have already more than once dwelt on the vividness with which he
realised molecular conditions; we have a fine example of this
strength and brightness of imagination in the present 'speculation.'
He grapples with the notion that matter is made up of particles, not
in absolute contact, but surrounded by interatomic space.  'Space,'
he observes, 'must be taken as the only continuous part of a body so
constituted.  Space will permeate all masses of matter in every
direction like a net, except that in place of meshes it will form
cells, isolating each atom from its neighbours, itself only being
continuous.' 

Let us follow out this notion; consider, he argues, the case of a
non-conductor of electricity, such for example as shell-lac, with
its molecules, and intermolecular spaces running through the mass. 
In its case space must be an insulator; for if it were a conductor
it would resemble 'a fine metallic web,' penetrating the lac in
every direction.  But the fact is that it resembles the wax of black
sealing-wax, which surrounds and insulates the particles of
conducting carbon, interspersed throughout its mass.  In the case of
shell-lac, therefore, space is an insulator.

But now, take the case of a conducting metal.  Here we have, as
before, the swathing of space round every atom.  If space be an
insulator there can be no transmission of electricity from atom to
atom.  But there is transmission; hence space is a conductor.  Thus
he endeavours to hamper the atomic theory. 'The reasoning,' he says,
'ends in a subversion of that theory altogether; for if space be an
insulator it cannot exist in conducting bodies, and if it be a
conductor it cannot exist in insulating bodies.  Any ground of
reasoning,' he adds, as if carried away by the ardour of argument,
'which tends to such conclusions as these must in itself be false.'

He then tosses the atomic theory from horn to horn of his dilemmas. 
What do we know, he asks, of the atom apart from its force?
You imagine a nucleus which may be called a, and surround it by
forces which may be called m; 'to my mind the a or nucleus vanishes,
and the substance consists in the powers of m.  And indeed what
notion can we form of the nucleus independent of its powers?
What thought remains on which to hang the imagination of an a
independent of the acknowledged forces?' Like Boscovich,
he abolishes the atom, and puts a 'centre of force' in its place.

With his usual courage and sincerity he pushes his view to its
utmost consequences.  'This view of the constitution of matter,'
he continues, 'would seem to involve necessarily the conclusion that
matter fills all space, or at least all space to which gravitation
extends; for gravitation is a property of matter dependent on a
certain force, and it is this force which constitutes the matter. 
In that view matter is not merely mutually penetrable;[1] but each
atom extends, so to say, throughout the whole of the solar system,
yet always retaining its own centre of force.'

It is the operation of a mind filled with thoughts of this profound,
strange, and subtle character that we have to take into account in
dealing with Faraday's later researches.  A similar cast of thought
pervades a letter addressed by Faraday to Mr. Richard Phillips,
and published in the 'Philosophical Magazine' for May, 1846.  It is
entitled 'Thoughts on Ray-vibrations,' and it contains one of the
most singular speculations that ever emanated from a scientific
mind.  It must be remembered here, that though Faraday lived amid
such speculations he did not rate them highly, and that he was
prepared at any moment to change them or let them go.  They spurred
him on, but they did not hamper him.  His theoretic notions were
fluent; and when minds less plastic than his own attempted to render
those fluxional images rigid, he rebelled.  He warns Phillips
moreover, that from first to last, 'he merely threw out as matter
for speculation the vague impressions of his mind; for he gave
nothing as the result of sufficient consideration, or as the settled
conviction, or even probable conclusion at which he had arrived.'

The gist of this communication is that gravitating force acts in
lines across space, and that the vibrations of light and radiant
heat consist in the tremors of these lines of force.  'This notion,'
he says, 'as far as it is admitted, will dispense with the ether,
which, in another view is supposed to be the medium in which these
vibrations take place.' And he adds further on, that his view
'endeavours to dismiss the ether but not the vibrations.'  The idea
here set forth is the natural supplement of his previous notion,
that it is gravitating force which constitutes matter, each atom
extending, so to say, throughout the whole of the solar system.

The letter to Mr. Phillips winds up with this beautiful
conclusion:--

'I think it likely that I have made many mistakes in the preceding
pages, for even to myself my ideas on this point appear only as the
shadow of a speculation, or as one of those impressions upon the
mind which are allowable for a time as guides to thought and
research.  He who labours in experimental inquiries, knows how
numerous these are, and how often their apparent fitness and beauty
vanish before the progress and development of real natural truth.'

Let it then be remembered that Faraday entertained notions regarding
matter and force altogether distinct from the views generally held
by scientific men.  Force seemed to him an entity dwelling along the
line in which it is exerted.  The lines along which gravity acts
between the sun and earth seem figured in his mind as so many
elastic strings; indeed he accepts the assumed instantaneity of
gravity as the expression of the enormous elasticity of the 'lines
of weight.' Such views, fruitful in the case of magnetism, barren,
as yet, in the case of gravity, explain his efforts to transform
this latter force.  When he goes into the open air and permits his
helices to fall, to his mind's eye they are tearing through the
lines of gravitating power, and hence his hope and conviction that
an effect would and ought to be produced.  It must ever be borne in
mind that Faraday's difficulty in dealing with these conceptions was
at bottom the same as that of Newton; that he is in fact trying to
overleap this difficulty, and with it probably the limits prescribed
to the intellect itself.  

The idea of lines of magnetic force was suggested to Faraday by the
linear arrangement of iron filings when scattered over a magnet.
He speaks of and illustrates by sketches, the deflection, both
convergent and divergent, of the lines of force, when they pass
respectively through magnetic and diamagnetic bodies.  These notions
of concentration and divergence are also based on the direct
observation of his filings.  So long did he brood upon these lines;
so habitually did he associate them with his experiments on induced
currents, that the association became 'indissoluble,' and he could
not think without them.  'I have been so accustomed,' he writes,
'to employ them, and especially in my last researches, that I may
have unwittingly become prejudiced in their favour, and ceased to be
a clear-sighted judge. Still, I have always endeavoured to make
experiment the test and controller of theory and opinion; but
neither by that nor by close cross-examination in principle, have I
been made aware of any error involved in their use.'

In his later researches on magne-crystallic action, the idea of
lines of force is extensively employed; it indeed led him to an
experiment which lies at the root of the whole question.  In his
subsequent researches on Atmospheric Magnetism the idea receives
still wider application, showing itself to be wonderfully flexible
and convenient.  Indeed without this conception the attempt to seize
upon the magnetic actions, possible or actual, of the atmosphere
would be difficult in the extreme; but the notion of lines of force,
and of their divergence and convergence, guides Faraday without
perplexity through all the intricacies of the question.  After the
completion of those researches, and in a paper forwarded to the
Royal Society on October 22, 1851, he devotes himself to the formal
development and illustration of his favourite idea.  The paper bears
the title, 'On lines of magnetic force, their definite character,
and their distribution within a magnet and through space.'
A deep reflectiveness is the characteristic of this memoir.
In his experiments, which are perfectly beautiful and profoundly
suggestive, he takes but a secondary delight.  His object is to
illustrate the utility of his conception of lines of force.
'The study of these lines,' he says, 'has at different times been
greatly influential in leading me to various results which I think
prove their utility as well as fertility.'

Faraday for a long period used the lines of force merely as
'a representative idea.' He seemed for a time averse to going further
in expression than the lines themselves, however much further he may
have gone in idea.  That he believed them to exist at all times
round a magnet, and irrespective of the existence of magnetic
matter, such as iron filings, external to the magnet, is certain. 
No doubt the space round every magnet presented itself to his
imagination as traversed by loops of magnetic power; but he was
chary in speaking of the physical substratum of those loops.  Indeed
it may be doubted whether the physical theory of lines of force
presented itself with any distinctness to his own mind.
The possible complicity of the luminiferous ether in magnetic phenomena
was certainly in his thoughts.  'How the magnetic force,' he writes,
'is transferred through bodies or through space we know not; whether
the result is merely action at a distance, as in the case of gravity;
or by some intermediate agency, as in the case of light, heat,
the electric current, and (as I believe) static electric action.
The idea of magnetic fluids, as applied by some, or of Magnetic centres
of action, does not include that of the latter kind of transmission,
but the idea of lines of force does.' And he continues thus:--
'I am more inclined to the notion that in the transmission of the
[magnetic] force there is such an action [an intermediate agency]
external to the magnet, than that the effects are merely attraction
and repulsion at a distance.  Such an affection may be a function of
the ether; for it is not at all unlikely that, if there be an ether,
it should have other uses than simply the conveyance of radiations.'
When he speaks of the magnet in certain cases, 'revolving amongst
its own forces,' he appears to have some conception of this kind in
view.  

A great part of the investigation completed in October, 1851, was
taken up with the motions of wires round the poles of a magnet and
the converse.  He carried an insulated wire along the axis of a bar
magnet from its pole to its equator, where it issued from the magnet,
and was bent up so as to connect its two ends.  A complete circuit,
no part of which was in contact with the magnet, was thus obtained. 
He found that when the magnet and the external wire were rotated
together no current was produced; whereas, when either of them was
rotated and the other left at rest currents were evolved. He then
abandoned the axial wire, and allowed the magnet itself to take its
place; the result was the same.[2]  It was the relative motion of
the magnet and the loop that was effectual in producing a current.  

The lines of force have their roots in the magnet, and though they
may expand into infinite space, they eventually return to the magnet.
Now these lines may be intersected close to the magnet or at a
distance from it. Faraday finds distance to be perfectly immaterial
so long as the number of lines intersected is the same.
For example, when the loop connecting the equator and the pole of
his barmagnet performs one complete revolution round the magnet,
it is manifest that all the lines of force issuing from the magnet
are once intersected.  Now it matters not whether the loop be ten feet
or ten inches in length, it matters not how it may be twisted and
contorted, it matters not how near to the magnet or how distant from
it the loop may be, one revolution always produces the same amount
of current electricity, because in all these cases all the lines of
force issuing from the magnet are once intersected and no more.

From the external portion of the circuit he passes in idea to the
internal, and follows the lines of force into the body of the magnet
itself.  His conclusion is that there exist lines of force within
the magnet of the same nature as those without.  What is more, they
are exactly equal in amount to those without.  They have a relation
in direction to those without; and in fact are continuations of
them....  'Every line of force, therefore, at whatever distance it
may be taken from the magnet, must be considered as a closed
circuit, passing in some part of its course through the magnet,
and having an equal amount of force in every part of its course.'

All the results here described were obtained with moving metals. 
'But,' he continues with profound sagacity, 'mere motion would not
generate a relation, which had not a foundation in the existence of
some previous state; and therefore the quiescent metals must be in
some relation to the active centre of force,' that is to the magnet. 
He here touches the core of the whole question, and when we can
state the condition into which the conducting wire is thrown before
it is moved, we shall then be in a position to understand the
physical constitution of the electric current generated by its
motion.  

In this inquiry Faraday worked with steel magnets, the force of
which varies with the distance from the magnet.  He then sought a
uniform field of magnetic force, and found it in space as affected
by the magnetism of the earth.  His next memoir, sent to the Royal
Society, December 31, 1851, is 'on the employment of the Induced
Magnetoelectro Current as a test and measure of magnetic forces.'
He forms rectangles and rings, and by ingenious and simple devices
collects the opposed currents which are developed in them by
rotation across the terrestrial lines of magnetic force.  He varies
the shapes of his rectangles while preserving their areas constant,
and finds that the constant area produces always the same amount of
current per revolution.  The current depends solely on the number of
lines of force intersected, and when this number is kept constant
the current remains constant too.  Thus the lines of magnetic force
are continually before his eyes, by their aid he colligates his
facts, and through the inspirations derived from them he vastly
expands the boundaries of our experimental knowledge.  The beauty
and exactitude of the results of this investigation are
extraordinary.  I cannot help thinking while I dwell upon them, that
this discovery of magneto-electricity is the greatest experimental
result ever obtained by an investigator.  It is the Mont Blanc of
Faraday's own achievements.  He always worked at great elevations,
but a higher than this he never subsequently attained.  

Footnotes to Chapter 13

[1] He compares the interpenetration of two atoms to the
coalescence of two distinct waves, which though for a moment blended
to a single mass, preserve their individuality, and afterwards
separate.

[2] In this form the experiment is identical with one made twenty
years earlier.  See page 34.


Chapter 14.

Unity and convertibility of natural forces:
theory of the electric current.

The terms unity and convertibility, as applied to natural forces,
are often employed in these investigations, many profound and
beautiful thoughts respecting these subjects being expressed in
Faraday's memoirs.  Modern inquiry has, however, much augmented our
knowledge of the relationship of natural forces, and it seems worth
while to say a few words here, tending to clear up certain
misconceptions which appear to exist among philosophic writers
regarding this relationship.  

The whole stock of energy or working-power in the world consists of
attractions, repulsions, and motions.  If the attractions and
repulsions are so circumstanced as to be able to produce motion,
they are sources of working-power, but not otherwise.  Let us for
the sake of simplicity confine our attention to the case of
attraction.  The attraction exerted between the earth and a body at
a distance from the earth's surface is a source of working-power;
because the body can be moved by the attraction, and in falling to
the earth can perform work.  When it rests upon the earth's surface
it is not a source of power or energy, because it can fall no
further.  But though it has ceased to be a source of energy, the
attraction of gravity still acts as a force, which holds the earth
and weight together.  

The same remarks apply to attracting atoms and molecules.  As long
as distance separates them, they can move across it in obedience to
the attraction, and the motion thus produced may, by proper appliances,
be caused to perform mechanical work.  When, for example, two atoms
of hydrogen unite with one of oxygen, to form water the atoms are
first drawn towards each other--they move, they clash, and then by
virtue of their resiliency, they recoil and quiver.  To this
quivering motion we give the name of heat.  Now this quivering
motion is merely the redistribution of the motion produced by the
chemical affinity; and this is the only sense in which chemical
affinity can be said to be converted into heat.  We must not imagine
the chemical attraction destroyed, or converted into anything else. 
For the atoms, when mutually clasped to form a molecule of water,
are held together by the very attraction which first drew them
towards each other.  That which has really been expended is the pull
exerted through the space by which the distance between the atoms
has been diminished.  

If this be understood, it will be at once seen that gravity may in
this sense be said to be convertible into heat; that it is in
reality no more an outstanding and inconvertible agent, as it is
sometimes stated to be, than chemical affinity.  By the exertion of
a certain pull, through a certain space, a body is caused to clash
with a certain definite velocity against the earth.  Heat is thereby
developed, and this is the only sense in which gravity can be said
to be converted into heat.  In no case is the force which produces
the motion annihilated or changed into anything else.  The mutual
attraction of the earth and weight exists when they are in contact
as when they were separate; but the ability of that attraction to
employ itself in the production of motion does not exist.

The transformation, in this case, is easily followed by the mind's
eye. First, the weight as a whole is set in motion by the attraction
of gravity. This motion of the mass is arrested by collision with
the earth; being broken up into molecular tremors, to which we give
the name of heat.

And when we reverse the process, and employ those tremors of heat to
raise a weight, as is done through the intermediation of an elastic
fluid in the steam-engine, a certain definite portion of the
molecular motion is destroyed in raising the weight.  In this sense,
and this sense only, can the heat be said to be converted into
gravity, or more correctly, into potential energy of gravity.  It is
not that the destruction of the heat has created any new attraction,
but simply that the old attraction has now a power conferred upon it,
of exerting a certain definite pull in the interval between the
starting-point of the falling weight and its collision with the earth.  

So also as regards magnetic attraction: when a sphere of iron placed
at some distance from a magnet rushes towards the magnet, and has
its motion stopped by collision, an effect mechanically the same as
that produced by the attraction of gravity occurs.  The magnetic
attraction generates the motion of the mass, and the stoppage of
that motion produces heat.  In this sense, and in this sense only,
is there a transformation of magnetic work into heat.  And if by the
mechanical action of heat, brought to bear by means of a suitable
machine, the sphere be torn from the magnet and again placed at a
distance, a power of exerting a pull through that distance, and
producing a new motion of the sphere, is thereby conferred upon the
magnet; in this sense, and in this sense only, is the heat converted
into magnetic potential energy.  

When, therefore, writers on the conservation of energy speak of
tensions being 'consumed' and 'generated,' they do not mean thereby
that old attractions have been annihilated and new ones brought into
existence, but that, in the one case, the power of the attraction to
produce motion has been diminished by the shortening of the distance
between the attracting bodies, and that in the other case the power
of producing motion has been augmented by the increase of the
distance.  These remarks apply to all bodies, whether they be
sensible masses or molecules.  

Of the inner quality that enables matter to attract matter we know
nothing; and the law of conservation makes no statement regarding
that quality.  It takes the facts of attraction as they stand, and
affirms only the constancy of working-power.  That power may exist
in the form of MOTION; or it may exist in the form of FORCE, with
distance to act through.  The former is dynamic energy, the latter
is potential energy, the constancy of the sum of both being affirmed
by the law of conservation.  The convertibility of natural forces
consists solely in transformations of dynamic into potential, and of
potential into dynamic, energy, which are incessantly going on.
In no other sense has the convertibility of force, at present,
any scientific meaning.  

By the contraction of a muscle a man lifts a weight from the earth. 
But the muscle can contract only through the oxidation of its own
tissue or of the blood passing through it.  Molecular motion is thus
converted into mechanical motion.  Supposing the muscle to contract
without raising the weight, oxidation would also occur, but the
whole of the heat produced by this oxidation would be liberated in
the muscle itself.  Not so when it performs external work; to do
that work a certain definite portion of the heat of oxidation must
be expended.  It is so expended in pulling the weight away from the
earth.  If the weight be permitted to fall, the heat generated by
its collision with the earth would exactly make up for that lacking
in the muscle during the lifting of the weight.  In the case here
supposed, we have a conversion of molecular muscular action into
potential energy of gravity; and a conversion of that potential
energy into heat; the heat, however, appearing at a distance from
its real origin in the muscle.  The whole process consists of a
transference of molecular motion from the muscle to the weight,
and gravitating force is the mere go-between, by means of which the
transference is effected.  

These considerations will help to clear our way to the conception of
the transformations which occur when a wire is moved across the
lines of force in a magnetic field.  In this case it is commonly
said we have a conversion of magnetism into electricity.  But let us
endeavour to understand what really occurs.  For the sake of
simplicity, and with a view to its translation into a different one
subsequently, let us adopt for a moment the provisional conception
of a mixed fluid in the wire, composed of positive and negative
electricities in equal quantities, and therefore perfectly
neutralizing each other when the wire is still.  By the motion of
the wire, say with the hand, towards the magnet, what the Germans
call a Scheidungs-Kraft--a separating force--is brought into play. 
This force tears the mixed fluids asunder, and drives them in two
currents, the one positive and the other negative, in two opposite
directions through the wire.  The presence of these currents evokes
a force of repulsion between the magnet and the wire; and to cause
the one to approach the other, this repulsion must be overcome.
The overcoming of this repulsion is, in fact, the work done in
separating and impelling the two electricities.  When the wire is
moved away from the magnet, a Scheidungs-Kraft, or separating force,
also comes into play; but now it is an attraction that has to be
surmounted.  In surmounting it, currents are developed in directions
opposed to the former; positive takes the place of negative, and
negative the place of positive; the overcoming of the attraction
being the work done in separating and impelling the two
electricities.  

The mechanical action occurring here is different from that
occurring where a sphere of soft iron is withdrawn from a magnet,
and again attracted.  In this case muscular force is expended during
the act of separation; but the attraction of the magnet effects the
reunion.  In the case of the moving wire also we overcome a
resistance in separating it from the magnet, and thus far the action
is mechanically the same as the separation of the sphere of iron.
But after the wire has ceased moving, the attraction ceases; and so
far from any action occurring similar to that which draws the iron
sphere back to the magnet, we have to overcome a repulsion to bring
them together.  

There is no potential energy conferred either by the removal or by
the approach of the wire, and the only power really transformed or
converted, in the experiment, is muscular power.  Nothing that could
in strictness be called a conversion of magnetism into electricity
occurs.  The muscular oxidation that moves the wire fails to produce
within the muscle its due amount of heat, a portion of that heat,
equivalent to the resistance overcome, appearing in the moving wire
instead.  

Is this effect an attraction and a repulsion at a distance?  If so,
why should both cease when the wire ceases to move? In fact, the
deportment of the wire resembles far more that of a body moving in a
resisting medium than anything else; the resistance ceasing when the
motion is suspended.  Let us imagine the case of a liquid so mobile
that the hand may be passed through it to and fro, without
encountering any sensible resistance.  It resembles the motion of a
conductor in the unexcited field of an electro-magnet.  Now, let us
suppose a body placed in the liquid, or acting on it, which confers
upon it the property of viscosity; the hand would no longer move
freely. During its motion, but then only, resistance would be
encountered and overcome.  Here we have rudely represented the case
of the excited magnetic field, and the result in both cases would be
substantially the same.  In both cases heat would, in the end, be
generated outside of the muscle, its amount being exactly equivalent
to the resistance overcome.

Let us push the analogy a little further; suppose in the case of the
fluid rendered viscous, as assumed a moment ago, the viscosity not
to be so great as to prevent the formation of ripples when the hand
is passed through the liquid.  Then the motion of the hand, before
its final conversion into heat, would exist for a time as
wave-motion, which, on subsiding, would generate its due equivalent
of heat.  This intermediate stage, in the case of our moving wire,
is represented by the period during which the electric current is
flowing through it; but that current, like the ripples of our
liquid, soon subsides, being, like them, converted into heat.

Do these words shadow forth anything like the reality?  Such
speculations cannot be injurious if they are enunciated without
dogmatism.  I do confess that ideas such as these here indicated
exercise a strong fascination on my mind.  Is then the magnetic
field really viscous, and if so, what substance exists in it and the
wire to produce the viscosity?  Let us first look at the proved
effects, and afterwards turn our thoughts back upon their cause. 
When the wire approaches the magnet, an action is evoked within it,
which travels through it with a velocity comparable to that of light.
One substance only in the universe has been hitherto proved
competent to transmit power at this velocity; the luminiferous
ether.  Not only its rapidity of progression, but its ability to
produce the motion of light and heat, indicates that the electric
current is also motion.[1] Further, there is a striking resemblance
between the action of good and bad conductors as regards electricity,
and the action of diathermanous and adiathermanous bodies as regards
radiant heat.  The good conductor is diathermanous to the electric
current; it allows free transmission without the development of
heat.  The bad conductor is adiathermanous to the electric current,
and hence the passage of the latter is accompanied by the
development of heat.  I am strongly inclined to hold the electric
current, pure and simple, to be a motion of the ether alone; good
conductors being so constituted that the motion may be propagated
through their ether without sensible transfer to their atoms, while
in the case of bad conductors this transfer is effected, the
transferred motion appearing as heat.[2] 

I do not know whether Faraday would have subscribed to what is here
written; probably his habitual caution would have prevented him from
committing himself to anything so definite.  But some such idea
filled his mind and coloured his language through all the later
years of his life.  I dare not say that he has been always
successful in the treatment of these theoretic notions.  In his
speculations he mixes together light and darkness in varying
proportions, and carries us along with him through strong
alternations of both.  It is impossible to say how a certain amount
of mathematical training would have affected his work.  We cannot
say what its influence would have been upon that force of
inspiration that urged him on; whether it would have daunted him,
and prevented him from driving his adits into places where no theory
pointed to a lode.  If so, then we may rejoice that this strong
delver at the mine of natural knowledge was left free to wield his
mattock in his own way.  It must be admitted, that Faraday's purely
speculative writings often lack that precision which the
mathematical habit of thought confers. Still across them flash
frequent gleams of prescient wisdom which will excite admiration
throughout all time; while the facts, relations, principles, and
laws which his experiments have established are sure to form the
body of grand theories yet to come.

Footnotes to Chapter 14

[1] Mr. Clerk Maxwell has recently published an exceedingly
important investigation connected with this question.  Even in the
non-mathematical portions of the memoirs of Mr. Maxwell,
the admirable spirit of his philosophy is sufficiently revealed.
As regards the employment of scientific imagery, I hardly know his
equal in power of conception and clearness of definition.

[2] One important difference, of course, exists between the effect
of motion in the magnetic field, and motion in a resisting medium. 
In the former case the heat is generated in the moving conductor,
in the latter it is in part generated in the medium.


Chapter 15.

  Summary.

When from an Alpine height the eye of the climber ranges over the
mountains, he finds that for the most part they resolve themselves
into distinct groups, each consisting of a dominant mass surrounded
by peaks of lesser elevation. The power which lifted the mightier
eminences, in nearly all cases lifted others to an almost equal
height.  And so it is with the discoveries of Faraday.  As a general
rule, the dominant result does not stand alone, but forms the
culminating point of a vast and varied mass of inquiry.  In this
way, round about his great discovery of Magneto-electric Induction,
other weighty labours group themselves.  His investigations on the
Extra Current; on the Polar and other Condition of Diamagnetic
Bodies; on Lines of Magnetic Force, their definite character and
distribution; on the employment of the Induced Magneto-electric
Current as a measure and test of Magnetic Action; on the Revulsive
Phenomena of the magnetic field, are all, notwithstanding the
diversity of title, researches in the domain of Magneto-electric
Induction.  

Faraday's second group of researches and discoveries embrace the
chemical phenomena of the current.  The dominant result here is the
great law of definite Electro-chemical Decomposition, around which
are massed various researches on Electro-chemical Conduction and on
Electrolysis both with the Machine and with the Pile.  To this group
also belongs his analysis of the Contact Theory, his inquiries as to
the Source of Voltaic Electricity, and his final development of the
Chemical Theory of the pile.  

His third great discovery is the Magnetization of Light, which I
should liken to the Weisshorn among mountains--high, beautiful,
and alone.  

The dominant result of his fourth group of researches is the
discovery of Diamagnetism, announced in his memoir as the Magnetic
Condition of all Matter, round which are grouped his inquiries on
the Magnetism of Flame and Gases; on Magne-crystallic action, and on
Atmospheric Magnetism, in its relations to the annual and diurnal
variation of the needle, the full significance of which is still to
be shown.  

These are Faraday's most massive discoveries, and upon them his fame
must mainly rest.  But even without them, sufficient would remain to
secure for him a high and lasting scientific reputation.  We should
still have his researches on the Liquefaction of Gases; on
Frictional Electricity; on the Electricity of the Gymnotus; on the
source of Power in the Hydro-electric machine, the last two
investigations being untouched in the foregoing memoir; on
Electro-magnetic Rotations; on Regelation; all his more purely
Chemical Researches, including his discovery of Benzol.  Besides
these he published a multitude of minor papers, most of which, in
some way or other, illustrate his genius.  I have made no allusion
to his power and sweetness as a lecturer.  Taking him for all in
all, I think it will be conceded that Michael Faraday was the
greatest experimental philosopher the world has ever seen; and I
will add the opinion, that the progress of future research will
tend, not to dim or to diminish, but to enhance and glorify the
labours of this mighty investigator.  


Chapter 16.

 Illustrations of Character.

Thus far I have confined myself to topics mainly interesting to the
man of science, endeavouring, however, to treat them in a manner
unrepellent to the general reader who might wish to obtain a notion
of Faraday as a worker.  On others will fall the duty of presenting
to the world a picture of the man. But I know you will permit me to
add to the foregoing analysis a few personal reminiscences and
remarks, tending to connect Faraday with a wider world than that of
science--namely, with the general human heart.

One word in reference to his married life, in addition to what has
been already said, may find a place here.  As in the former case,
Faraday shall be his own spokesman.  The following paragraph, though
written in the third person, is from his hand:--'On June 12, 1821,
he married, an event which more than any other contributed to his
earthly happiness and healthful state of mind.  The union has
continued for twenty-eight years and has in no wise changed, except
in the depth and strength of its character.'

Faraday's immediate forefathers lived in a little place called
Clapham Wood Hall, in Yorkshire.  Here dwelt Robert Faraday and
Elizabeth his wife, who had ten children, one of them, James
Faraday, born in 1761, being father to the philosopher.  A family
tradition exists that the Faradays came originally from Ireland. 
Faraday himself has more than once expressed to me his belief that
his blood was in part Celtic, but how much of it was so, or when the
infusion took place, he was unable to say.  He could imitate the
Irish brogue, and his wonderful vivacity may have been in part due
to his extraction.  But there were other qualities which we should
hardly think of deriving from Ireland.  The most prominent of these
was his sense of order, which ran like a luminous beam through all
the transactions of his life.  The most entangled and complicated
matters fell into harmony in his hands.  His mode of keeping
accounts excited the admiration of the managing board of this
Institution.  And his science was similarly ordered.  In his
Experimental Researches, he numbered every paragraph, and welded
their various parts together by incessant reference.  His private
notes of the Experimental Researches, which are happily preserved,
are similarly numbered: their last paragraph bears the figure 16,041.
His working qualities, moreover, showed the tenacity of the Teuton. 
His nature was impulsive, but there was a force behind the impulse
which did not permit it to retreat.  If in his warm moments he
formed a resolution, in his cool ones he made that resolution good. 
Thus his fire was that of a solid combustible, not that of a gas,
which blazes suddenly, and dies as suddenly away.  

And here I must claim your tolerance for the limits by which I am
confined. No materials for a life of Faraday are in my hands, and
what I have now to say has arisen almost wholly out of our close
personal relationship.  

Letters of his, covering a period of sixteen years, are before me,
each one of which contains some characteristic utterance;--strong,
yet delicate in counsel, joyful in encouragement, and warm in
affection.  References which would be pleasant to such of them as
still live are made to Humboldt, Biot, Dumas, Chevreul, Magnus, and
Arago.  Accident brought these names prominently forward; but many
others would be required to complete his list of continental
friends.  He prized the love and sympathy of men--prized it almost
more than the renown which his science brought him.  Nearly a dozen
years ago it fell to my lot to write a review of his 'Experimental
Researches' for the 'Philosophical Magazine.'  After he had read it,
he took me by the hand, and said, 'Tyndall, the sweetest reward of
my work is the sympathy and good will which it has caused to flow in
upon me from all quarters of the world.'  Among his letters I find
little sparks of kindness, precious to no one but myself, but more
precious to me than all.  He would peep into the laboratory when he
thought me weary, and take me upstairs with him to rest.  And if I
happened to be absent, he would leave a little note for me, couched
in this or some other similar form:--
'Dear Tyndall,--I was looking for you, because we were at tea--
we have not yet done--will you come up?' I frequently shared his
early dinner; almost always, in fact, while my lectures were going on. 
There was no trace of asceticism in his nature.  He preferred the
meat and wine of life to its locusts and wild honey.  Never once
during an intimacy of fifteen years did he mention religion to me,
save when I drew him on to the subject.  He then spoke to me without
hesitation or reluctance; not with any apparent desire to 'improve
the occasion,' but to give me such information as I sought.
He believed the human heart to be swayed by a power to which science
or logic opened no approach, and, right or wrong, this faith, held in
perfect tolerance of the faiths of others, strengthened and
beautified his life.  

From the letters just referred to, I will select three for
publication here. I choose the first, because it contains a passage
revealing the feelings with which Faraday regarded his vocation, and
also because it contains an allusion which will give pleasure to a
friend.


'Royal Institution.  [ this is crossed out by Faraday ]

'Ventnor, Isle of Wight, June 28, 1854.  

'My Dear Tyndall,--You see by the top of this letter how much habit
prevails over me; I have just read yours from thence, and yet I
think myself there.  However, I have left its science in very good
keeping, and I am glad to learn that you are at experiment once
more.  But how is the health? Not well, I fear.  I wish you would
get yourself strong first and work afterwards.  As for the fruits, I
am sure they will be good, for though I sometimes despond as regards
myself, I do not as regards you.  You are young, I am old....
But then our subjects are so glorious, that to work at them rejoices
and encourages the feeblest; delights and enchants the strongest.  

'I have not yet seen anything from Magnus.  Thoughts of him always
delight me.  We shall look at his black sulphur together.  I heard
from Schonbein the other day.  He tells me that Liebig is full of
ozone, i.e., of allotropic oxygen.  

'Good-bye for the present.
   'Ever, my dear Tyndall,
       'Yours truly,
           'M. Faraday.'

The contemplation of Nature, and his own relation to her, produced
in Faraday a kind of spiritual exaltation which makes itself
manifest here.  His religious feeling and his philosophy could not
be kept apart; there was an habitual overflow of the one into the
other.

Whether he or another was its exponent, he appeared to take equal
delight in science.  A good experiment would make him almost dance
with delight.  In November, 1850, he wrote to me thus: --'I hope
some day to take up the point respecting the magnetism of associated
particles.  In the meantime I rejoice at every addition to the facts
and reasoning connected with the subject. When science is a
republic, then it gains: and though I am no republican in other
matters, I am in that.' All his letters illustrate this catholicity
of feeling.  Ten years ago, when going down to Brighton, he carried
with him a little paper I had just completed, and afterwards wrote
to me.  His letter is a mere sample of the sympathy which he always
showed to me and my work.


'Brighton, December 9, 1857.

'My Dear Tyndall,--I cannot resist the pleasure of saying how very
much I have enjoyed your paper.  Every part has given me delight. 
It goes on from point to point beautifully.  You will find many
pencil marks, for I made them as I read.  I let them stand, for
though many of them receive their answer as the story proceeds, yet
they show how the wording impresses a mind fresh to the subject, and
perhaps here and there you may like to alter it slightly, if you
wish the full idea, i.e., not an inaccurate one, to be suggested at
first; and yet after all I believe it is not your exposition, but
the natural jumping to a conclusion that affects or has affected my
pencil.  

'We return on Friday, when I will return you the paper.

'Ever truly yours,
'M.  Faraday.'


The third letter will come in its proper place towards the end.

While once conversing with Faraday on science, in its relations to
commerce and litigation, he said to me, that at a certain period of
his career, he was forced definitely to ask himself, and finally to
decide whether he should make wealth or science the pursuit of his
life.  He could not serve both masters, and he was therefore
compelled to choose between them.  After the discovery of
magneto-electricity his fame was so noised abroad, that the
commercial world would hardly have considered any remuneration too
high for the aid of abilities like his.  Even before he became so
famous, he had done a little 'professional business.' This was the
phrase he applied to his purely commercial work.  His friend,
Richard Phillips, for example, had induced him to undertake a number
of analyses, which produced, in the year 1830, an addition to his
income of more than a thousand pounds; and in 1831 a still greater
addition.  He had only to will it to raise in 1832 his professional
business income to 5000L. a year.  Indeed double this sum would be
a wholly insufficient estimate of what he might, with ease, have
realised annually during the last thirty years of his life.  

While restudying the Experimental Researches with reference to the
present memoir, the conversation with Faraday here alluded to came
to my recollection, and I sought to ascertain the period when the
question, 'wealth or science,' had presented itself with such
emphasis to his mind.  I fixed upon the year 1831 or 1832, for it
seemed beyond the range of human power to pursue science as he had
done during the subsequent years, and to pursue commercial work at
the same time.  To test this conclusion I asked permission to see
his accounts, and on my own responsibility, I will state the result. 
In 1832, his professional business income, instead of rising to
5000L., or more, fell from 1090L. 4s. to 155L. 9s. From this it
fell with slight oscillations to 92L. in 1837, and to zero in 1838. 
Between 1839 and 1845, it never, except in one instance, exceeded
22L.; being for the most part much under this.  The exceptional year
referred to was that in which he and Sir Charles Lyell were engaged
by Government to write a report on the Haswell Colliery explosion,
and then his business income rose to 112L.  From the end of 1845 to
the day of his death, Faraday's annual professional business income
was exactly zero.  Taking the duration of his life into account,
this son of a blacksmith, and apprentice to a bookbinder, had to
decide between a fortune of 150,000L. on the one side, and his
undowered science on the other.  He chose the latter, and died a
poor man.  But his was the glory of holding aloft among the nations
the scientific name of England for a period of forty years.  

The outward and visible signs of fame were also of less account to
him than to most men.  He had been loaded with scientific honours
from all parts of the world.  Without, I imagine, a dissentient
voice, he was regarded as the prince of the physical investigators
of the present age.  The highest scientific position in this country
he had, however, never filled.  When the late excellent and lamented
Lord Wrottesley resigned the presidency of the Royal Society, a
deputation from the council, consisting of his Lordship, Mr. Grove,
and Mr. Gassiot, waited upon Faraday, to urge him to accept the
president's chair.  All that argument or friendly persuasion could
do was done to induce him to yield to the wishes of the council,
which was also the unanimous wish of scientific men.  A knowledge of
the quickness of his own nature had induced in Faraday the habit of
requiring an interval of reflection, before he decided upon any
question of importance.  In the present instance he followed his
usual habit, and begged for a little time.  

On the following morning, I went up to his room and said on entering
that I had come to him with some anxiety of mind.  He demanded its
cause, and I responded:--'Lest you should have decided against the
wishes of the deputation that waited on you yesterday.'  'You would
not urge me to undertake this responsibility,' he said.  'I not only
urge you,' was my reply, 'but I consider it your bounden duty to
accept it.' He spoke of the labour that it would involve; urged that
it was not in his nature to take things easy; and that if he became
president, he would surely have to stir many new questions, and
agitate for some changes.  I said that in such cases he would find
himself supported by the youth and strength of the Royal Society. 
This, however, did not seem to satisfy him.  Mrs. Faraday came into
the room, and he appealed to her.  Her decision was adverse, and I
deprecated her decision.  'Tyndall,' he said at length, 'I must
remain plain Michael Faraday to the last; and let me now tell you,
that if I accepted the honour which the Royal Society desires to
confer upon me, I would not answer for the integrity of my intellect
for a single year.' I urged him no more, and Lord Wrottesley had a
most worthy successor in Sir Benjamin Brodie.  

After the death of the Duke of Northumberland, our Board of Managers
wished to see Mr. Faraday finish his career as President of the
Institution, which he had entered on weekly wages more than half a
century before.  But he would have nothing to do with the
presidency.  He wished for rest, and the reverent affection of his
friends was to him infinitely more precious than all the honours of
official life.  

The first requisite of the intellectual life of Faraday was the
independence of his mind; and though prompt to urge obedience where
obedience was due, with every right assertion of manhood he
intensely sympathized.  Even rashness on the side of honour found
from him ready forgiveness, if not open applause.  The wisdom of
years, tempered by a character of this kind, rendered his counsel
peculiarly precious to men sensitive like himself.  I often sought
that counsel, and, with your permission, will illustrate its
character by one or two typical instances.  

In 1855, I was appointed examiner under the Council for Military
Education. At that time, as indeed now, I entertained strong
convictions as to the enormous utility of physical science to
officers of artillery and engineers, and whenever opportunity
offered, I expressed this conviction without reserve.  I did not
think the recognition, though considerable, accorded to physical
science in those examinations at all proportionate to its
importance; and this probably rendered me more jealous than I
otherwise should have been of its claims.  

In Trinity College, Dublin, a school had been organized with
reference to the Woolwich examinations, and a large number of
exceedingly well-instructed young gentlemen were sent over from
Dublin, to compete for appointments in the artillery and the
engineers.  The result of one examination was particularly
satisfactory to me; indeed the marks obtained appeared so eloquent
that I forbore saying a word about them.  My colleagues, however,
followed the usual custom of sending in brief reports with their
returns of marks.  After the results were published, a leading
article appeared in 'The Times,' in which the reports were largely
quoted, praise being bestowed on all the candidates, except the
excellent young fellows who had passed through my hands.

A letter from Trinity College drew my attention to this article,
bitterly complaining that whereas the marks proved them to be the
best of all, the science candidates were wholly ignored.  I tried to
set matters right by publishing, on my own responsibility, a letter
in 'The Times.' The act, I knew, could not bear justification from
the War Office point of view; and I expected and risked the
displeasure of my superiors.  The merited reprimand promptly came. 
'Highly as the Secretary of State for War might value the expression
of Professor Tyndall's opinion, he begged to say that an examiner,
appointed by His Royal Highness the Commander-in-Chief, had no right
to appear in the public papers as Professor Tyndall has done,
without the sanction of the War Office.' Nothing could be more just
than this reproof, but I did not like to rest under it.  I wrote a
reply, and previous to sending it took it up to Faraday.  We sat
together before his fire, and he looked very earnest as he rubbed
his hands and pondered.  The following conversation then passed
between us:--

F. You certainly have received a reprimand, Tyndall; but the
   matter is over, and if you wish to accept the reproof, you will
   hear no more about it.

T. But I do not wish to accept it.

F. Then you know what the consequence of sending that letter will be?

T. I do.

F. They will dismiss you.

T. I know it.

F. Then send the letter!

The letter was firm, but respectful; it acknowledged the justice of
the censure, but expressed neither repentance nor regret.  Faraday,
in his gracious way, slightly altered a sentence or two to make it
more respectful still.  It was duly sent, and on the following day I
entered the Institution with the conviction that my dismissal was
there before me.  Weeks, however, passed.  At length the well-known
envelope appeared, and I broke the seal, not doubting the contents. 
They were very different from what I expected. 'The Secretary of
State for War has received Professor Tyndall's letter, and deems the
explanation therein given perfectly satisfactory.' I have often
wished for an opportunity of publicly acknowledging this liberal
treatment, proving, as it did, that Lord Panmure could discern and
make allowance for a good intention, though it involved an offence
against routine.  For many years subsequently it was my privilege to
act under that excellent body, the Council for Military Education.  

On another occasion of this kind, having encouraged me in a somewhat
hardy resolution I had formed, Faraday backed his encouragement by
an illustration drawn from his own life.  The subject will interest
you, and it is so sure to be talked about in the world, that no
avoidable harm can rise from its introduction here.  

In the year 1835, Sir Robert Peel wished to offer Faraday a pension,
but that great statesman quitted office before he was able to
realise his wish. The Minister who founded these pensions intended
them, I believe, to be marks of honour which even proud men might
accept without compromise of independence.  When, however, the
intimation first reached Faraday in an unofficial way, he wrote a
letter announcing his determination to decline the pension; and
stating that he was quite competent to earn his livelihood himself. 
That letter still exists, but it was never sent, Faraday's
repugnance having been overruled by his friends.  When Lord
Melbourne came into office, he desired to see Faraday; and probably
in utter ignorance of the man--for unhappily for them and us,
Ministers of State in England are only too often ignorant of great
Englishmen--his Lordship said something that must have deeply
displeased his visitor.  All the circumstances were once
communicated to me, but I have forgotten the details.  The term
'humbug,' I think, was incautiously employed by his Lordship, and
other expressions were used of a similar kind.  Faraday quitted the
Minister with his own resolves, and that evening he left his card
and a short and decisive note at the residence of Lord Melbourne,
stating that he had manifestly mistaken his Lordship's intention of
honouring science in his person, and declining to have anything
whatever to do with the proposed pension.  The good-humoured
nobleman at first considered the matter a capital joke; but he was
afterwards led to look at it more seriously.  An excellent lady,
who was a friend both to Faraday and the Minister, tried to arrange
matters between them; but she found Faraday very difficult to move
from the position he had assumed.  After many fruitless efforts,
she at length begged of him to state what he would require of Lord
Melbourne to induce him to change his mind.  He replied, 'I should
require from his Lordship what I have no right or reason to expect
that he would grant--a written apology for the words he permitted
himself to use to me.' The required apology came, frank and full,
creditable, I thought, alike to the Prime Minister and the
philosopher.  

Considering the enormous strain imposed on Faraday's intellect, the
boy-like buoyancy even of his later years was astonishing.  He was
often prostrate, but he had immense resiliency, which he brought
into action by getting away from London whenever his health failed. 
I have already indicated the thoughts which filled his mind during
the evening of his life.  He brooded on magnetic media and lines of
force; and the great object of the last investigation he ever
undertook was the decision of the question whether magnetic force
requires time for its propagation.  How he proposed to attack this
subject we may never know.  But he has left some beautiful apparatus
behind; delicate wheels and pinions, and associated mirrors, which
were to have been employed in the investigation.  The mere conception
of such an inquiry is an illustration of his strength and hopefulness,
and it is impossible to say to what results it might have led him. 
But the work was too heavy for his tired brain.  It was long before
he could bring himself to relinquish it and during this struggle he
often suffered from fatigue of mind.  It was at this period,
and before he resigned himself to the repose which marked the last
two years of his life, that he wrote to me the following letter--
one of many priceless letters now before me--which reveals, more than
anything another pen could express, the state of his mind at the time.
I was sometimes censured in his presence for my doings in the Alps,
but his constant reply was, 'Let him alone, he knows how to take
care of himself.'  In this letter, anxiety on this score reveals
itself for the first time.  


'Hampton Court, August 1, 1864.

'My Dear Tyndall,--I do not know whether my letter will catch you,
but I will risk it, though feeling very unfit to communicate with a
man whose life is as vivid and active as yours; but the receipt of
your kind letter makes me to know that, though I forget, I am not
forgotten, and though I am not able to remember at the end of a line
what was said at the beginning of it, the imperfect marks will
convey to you some sense of what I long to say.  We had heard of
your illness through Miss Moore, and I was therefore very glad to
learn that you are now quite well; do not run too many risks or make
your happiness depend too much upon dangers, or the hunting of them. 
Sometimes the very thinking of you, and what you may be about,
wearies me with fears, and then the cogitations pause and change,
but without giving me rest.  I know that much of this depends upon
my own worn-out nature, and I do not know why I write it, save that
when I write to you I cannot help thinking it, and the thoughts
stand in the way of other matter.  
  
*     *     *     *     *     *     *  

'See what a strange desultory epistle I am writing to you, and yet I
feel so weary that I long to leave my desk and go to the couch.

'My dear wife and Jane desire their kindest remembrances: I hear
them in the next room:...  I forget--but not you, my dear Tyndall, 
for I am 

'Ever yours,
'M. Faraday.'


This weariness subsided when he relinquished his work, and I have a
cheerful letter from him, written in the autumn of 1865.  But
towards the close of that year he had an attack of illness, from
which he never completely rallied.  He continued to attend the
Friday Evening Meetings, but the advance of infirmity was apparent
to us all.  Complete rest became finally essential to him, and he
ceased to appear among us.  There was no pain in his decline to
trouble the memory of those who loved him.  Slowly and peacefully he
sank towards his final rest, and when it came, his death was a
falling asleep.  In the fulness of his honours and of his age he
quitted us; the good fight fought, the work of duty--shall I not say
of glory?--done.  The 'Jane' referred to in the foregoing letter is
Faraday's niece, Miss Jane Barnard, who with an affection raised
almost to religious devotion watched him and tended him to the end.  

I saw Mr. Faraday for the first time on my return from Marburg in 1850.
I came to the Royal Institution, and sent up my card, with a copy of
the paper which Knoblauch and myself had just completed.  He came
down and conversed with me for half an hour.  I could not fail to
remark the wonderful play of intellect and kindly feeling exhibited
by his countenance.  When he was in good health the question of his
age would never occur to you.  In the light and laughter of his eyes
you never thought of his grey hairs.  He was then on the point of
publishing one of his papers on Magnecrystallic action, and he had
time to refer in a flattering Note to the memoir I placed in his
hands. I returned to Germany, worked there for nearly another year,
and in June, 1851, came back finally from Berlin to England.  Then,
for the first time,  and on my way to the meeting of the British
Association, at Ipswich, I met a man who has since made his mark
upon the intellect of his time; who has long been, and who by the
strong law of natural affinity must continue to be, a brother to me. 
We were both without definite outlook at the time, needing proper
work, and only anxious to have it to perform.  The chairs of Natural
History and of Physics being advertised as vacant in the University
of Toronto, we applied for them, he for the one, I for the other;
but, possibly guided by a prophetic instinct, the University
authorities declined having anything to do with either of us.
If I remember aright, we were equally unlucky elsewhere.  

One of Faraday's earliest letters to me had reference to this
Toronto business, which he thought it unwise in me to neglect. 
But Toronto had its own notions, and in 1853, at the instance of
Dr. Bence Jones, and on the recommendation of Faraday himself,
a chair of Physics at the Royal Institution was offered to me.
I was tempted at the same time to go elsewhere, but a strong
attraction drew me to his side.  Let me say that it was mainly his
and other friendships, precious to me beyond all expression, that
caused me to value my position here more highly than any other that
could be offered to me in this land.  Nor is it for its honour,
though surely that is great, but for the strong personal ties that
bind me to it, that I now chiefly prize this place.  You might not
credit me were I to tell you how lightly I value the honour of being
Faraday's successor compared with the honour of having been
Faraday's friend.  His friendship was energy and inspiration;
his 'mantle' is a burden almost too heavy to be borne.  

Sometimes during the last year of his life, by the permission or
invitation of Mrs. Faraday, I went up to his rooms to see him.
The deep radiance, which in his time of strength flashed with such
extraordinary power from his countenance, had subsided to a calm and
kindly light, by which my latest memory of him is warmed and
illuminated.  I knelt one day beside him on the carpet and placed my
hand upon his knee; he stroked it affectionately, smiled, and
murmured, in a low soft voice, the last words that I remember as
having been spoken to me by Michael Faraday.  

It was my wish and aspiration to play the part of Schiller to this
Goethe: and he was at times so strong and joyful--his body so
active, and his intellect so clear--as to suggest to me the thought
that he, like Goethe, would see the younger man laid low.  Destiny
ruled otherwise, and now he is but a memory to us all.  Surely no
memory could be more beautiful.  He was equally rich in mind and
heart.  The fairest traits of a character sketched by Paul, found in
him perfect illustration.  For he was 'blameless, vigilant, sober,
of good behaviour, apt to teach, not given to filthy lucre.'  He had
not a trace of worldly ambition; he declared his duty to his
Sovereign by going to the levee once a year, but beyond this he
never sought contact with the great.  The life of his spirit and of
his intellect was so full, that the things which men most strive
after were absolutely indifferent to him.  'Give me health and a
day,' says the brave Emerson, 'and I will make the pomp of emperors
ridiculous.' In an eminent degree Faraday could say the same.
What to him was the splendour of a palace compared with a
thunderstorm upon Brighton Downs?--what among all the appliances of
royalty to compare with the setting sun? I refer to a thunderstorm
and a sunset, because these things excited a kind of ecstasy in his
mind, and to a mind open to such ecstasy the pomps and pleasures of
the world are usually of small account. Nature, not education,
rendered Faraday strong and refined.  A favourite experiment of his
own was representative of himself.  He loved to show that water in
crystallizing excluded all foreign ingredients, however intimately
they might be mixed with it.  Out of acids, alkalis, or saline
solutions, the crystal came sweet and pure.  By some such natural 
process in the formation of this man, beauty and nobleness coalesced,
to the exclusion of everything vulgar and low.  He did not learn his
gentleness in the world, for he withdrew himself from its culture;
and still this land of England contained no truer gentleman than he. 
Not half his greatness was incorporate in his science, for science
could not reveal the bravery and delicacy of his heart.  

But it is time that I should end these weak words, and lay my poor
garland on the grave of this 

    Just and faithful knight of God.





End of Project Gutenberg Etext of Faraday As A Discoverer, by Tyndall